feat(files): raise the download cap to 2GB and stream /api/download

The 50MB cap on file-raw, the attachment /raw route and /api/download was
memory protection for a `readFile()` that no longer exists: file-raw and
/raw were rewritten to stream through `sendFileBody()` and answer Range
requests, so size costs a read stream rather than RSS (measured: a 600MB
download moved peak RSS by ~37MB). All the cap still did was refuse
legitimate downloads of build artifacts, videos and archives.

It is now MAX_FILE_DOWNLOAD_BYTES in config/buffer-limits.ts, default 2GB,
env CODEMAN_MAX_DOWNLOAD_BYTES, 0 = unlimited. `parseByteLimitEnv()` is
separate from the `parseInt(...) || default` idiom used elsewhere in that
file precisely because that idiom reads 0 as falsy and would silently
restore the default for the one value that means "no limit".

/api/download was the last route that really did buffer the whole file. It
now shares sendFileBody() with the other two, so it streams, advertises
Accept-Ranges, and is resumable. Its Content-Disposition also goes through
buildContentDisposition() rather than raw interpolation.

Refusals move from 400 to 413 across all three, which is the correct status
for the case; with the cap at 2GB it is a path almost nothing reaches now.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -270,7 +270,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 
 **Files panel search** (COD-236, the `q` param on `GET /api/sessions/:id/files`): `compileFileQuery()` (`utils/file-query.ts`, pure, no IO, so it unit-tests directly) compiles the query into a reusable predicate, which is what lets the server-side walk prune instead of streaming the whole tree. ⚠️ **A query turns that endpoint into a FLAT match list rather than a nested tree**, and the walk deliberately recurses past non-matching directories, since the whole point of searching is to reach a file whose ancestors do not match. An empty or whitespace-only query compiles to `null`, which is what keeps the default tree response byte-identical when no search is requested. ⚠️ **Globs are never compiled into a RegExp**: `*a*a*a…` translated to `^.*a.*a.*a…$` is a classic backtracking blowup evaluated synchronously against every walked path, so one pathological query would freeze the event loop for the whole server (the same reason `search-service.ts` is regex-free). `globMatch()` is a two-pointer wildcard walk instead, O(text · pattern) with both operands short by construction, and an overlong query (`MAX_QUERY_LENGTH`, 256) also compiles to `null` rather than running. A query containing `/` matches the relative path, otherwise the bare entry name; globs match anchored and case-insensitively (`*` spans any run, slashes included, `?` exactly one character), everything else is a plain case-insensitive substring.
 
-**Raw file bodies are streamed and range-aware**: `file-raw` and the attachments `/raw` route always advertise `Accept-Ranges: bytes` and answer a `Range` header with `206` + `Content-Range` (single-range only; parser is pure + unit-tested in `src/web/http-range.ts`, a malformed spec is ignored → 200 while an out-of-bounds one is a 416). ⚠️ A 200-only response is what made the File Viewer's `<video>` unseekable: Chrome then reports `video.seekable` as `[0, 0]`, the scrub bar is inert and `currentTime = x` silently reverts (measured on an 18MB mp4), and Safari refuses to start the media at all. ⚠️ These bodies go out through `reply.hijack()`, which bypasses Fastify's status handling — `sendRawStream` must copy the status onto `reply.raw` by hand or a partial body ships labelled `200` and the browser treats a slice as the whole file. ⚠️ Closing the preview must **pause and unload** the media (`_stopFilePreviewMedia` in panels-ui.js): dropping the overlay's `visible` class is `display:none` and nothing else, and a DETACHED `HTMLMediaElement` keeps playing, which is how the X button used to leave a video audible with no player to pause.
+**Raw file bodies are streamed and range-aware**: `file-raw`, the attachments `/raw` route and `GET /api/download` always advertise `Accept-Ranges: bytes` and answer a `Range` header with `206` + `Content-Range` (single-range only; parser is pure + unit-tested in `src/web/http-range.ts`, a malformed spec is ignored → 200 while an out-of-bounds one is a 416). ⚠️ **The size cap on all three is a sanity bound, not memory protection** (`MAX_FILE_DOWNLOAD_BYTES` in `config/buffer-limits.ts`, default 2GB, env `CODEMAN_MAX_DOWNLOAD_BYTES`, `0` = unlimited): the bodies stream, so size costs a read stream and not RSS (measured: a 600MB download moved peak RSS by ~37MB). Its predecessor was a hardcoded 50MB whose comment still said "prevent memory exhaustion" long after the `readFile()` it described was replaced by `sendFileBody()`, so all it did was refuse legitimate downloads of build artifacts, videos and archives. `/api/download` was the last route that really did buffer the whole file, and now shares `sendFileBody()` with the other two. ⚠️ A 200-only response is what made the File Viewer's `<video>` unseekable: Chrome then reports `video.seekable` as `[0, 0]`, the scrub bar is inert and `currentTime = x` silently reverts (measured on an 18MB mp4), and Safari refuses to start the media at all. ⚠️ These bodies go out through `reply.hijack()`, which bypasses Fastify's status handling — `sendRawStream` must copy the status onto `reply.raw` by hand or a partial body ships labelled `200` and the browser treats a slice as the whole file. ⚠️ Closing the preview must **pause and unload** the media (`_stopFilePreviewMedia` in panels-ui.js): dropping the overlay's `visible` class is `display:none` and nothing else, and a DETACHED `HTMLMediaElement` keeps playing, which is how the X button used to leave a video audible with no player to pause.
 
 **Ultracode / workflow-run visualization** (opt-in, default OFF): the Workflow tool writes a completion artifact only at run *end*, so live in-flight runs exist solely as transcript dirs. `workflow-run-watcher.ts` therefore synthesizes ACTIVE runs from transcripts until the completion artifact appears and supersedes them. It is **STANDALONE** and deliberately never imports or touches `subagent-watcher.ts`, despite reading the same tree. Two independent toggles: `showUltracodeAgents` (docked panel) and `ultracodeFloatingWindows` (floating windows); the watcher starts if **either** is on. → [architecture-invariants#ultracode--workflow-run-visualization](docs/architecture-invariants.md#ultracode-and-workflow-run-visualization)