feat(cases): clone a Git repository as a new case (#236)

Adds an Add Case -> "Clone Repo" tab plus two endpoints, implementing
@DodgyBadger's proposal in #236: clone a public repository straight into
codeman-cases/<name> and register it as a normal local case.

POST /api/cases/clone is synchronous by design (request held open, bounded
by GIT_CLONE_TIMEOUT_MS): no job store, no polling, no cancellation
surface. Success broadcasts the usual case:created event, so the case
still appears when a proxy idle-timeout kills the request mid-clone.

POST /api/cases/clone-preflight runs `git ls-remote --symref` so the UI can
say, while the user is still typing, whether the URL is cloneable without
credentials, what its default branch is, and which branches/tags exist.

Core lives in src/git-clone.ts, split into a pure half (URL parse, argv/env,
ls-remote parse, stderr classification) and a thin IO half, so every
security decision is unit-testable without spawning anything:

- `<name>::<payload>` transports are refused as a family, not by name:
  ext:: is the famous one, but any of them dispatches to git-remote-<name>
  and turns a clone into arbitrary command execution.
- A leading `-` is refused AND every spawn puts `--` before the operands.
  Either alone is one edit away from being a hole.
- argv arrays, never a shell. URLs carrying user:password@ are refused.
- gitNonInteractiveEnv() closes all four ways git can block on a prompt
  with no terminal attached (terminal prompt, askpass/GUI, ssh, GCM).
  HOME/PATH stay inherited, so a user's own credential helper or ssh agent
  keeps working; Codeman itself collects and stores nothing.
- The timeout signals the process GROUP, since clone fans out into
  git-remote-https/index-pack children that outlive a signal to the parent.
- Bounded output (redacted stderr tail, capped ls-remote stdout, 500 refs
  each) and a global 2-op pool, so N large clones cannot exhaust the host.

Repository contents beat scaffolding: an existing CLAUDE.md is kept, hooks
are merged into whatever .claude/settings.local.json the repo shipped, and
a repo that ships its own Claude settings is reported back as a warning
(those hooks run locally as soon as a session starts there). A failed clone
removes only the directory the attempt created, and refuses a pre-existing
destination outright, so it can never squat on a case name.

Not admin-gated in multi-user mode, unlike /api/cases/link: it writes only
inside the caller's own case space. Local-path/file:// sources are the
exception and stay admin-only there.

UI: live verdict under the URL field, case name filled from the parsed repo
until the user types their own, branch/tag as a datalist of the remote's
real refs, optional shallow clone, and a Brain picker (installed CLIs only)
that points the Run button at the chosen agent. Starting a session stays
opt-in. The tab hides itself when the server reports no git.

Tests: the pure half exhaustively (every refusal has a case), plus real git
against a real local bare repo for clone/ref/timeout/cleanup, and a
route-level suite with unmocked fs that clones through the endpoint.

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

src/web/schemas.ts

@@ -366,6 +366,31 @@ export const CreateCaseSchema = z.object({
   description: z.string().max(1000).optional(),
 });
 
+/**
+ * Schema for POST /api/cases/clone — issue #236.
+ *
+ * `repository` is only length-bounded here on purpose: what makes an operand safe
+ * is the transport/shape analysis in `parseGitRepositoryUrl` (which also produces
+ * the user-facing rejection reason), and duplicating a weaker version of that as a
+ * regex would be the copy that drifts. The route parses before touching git.
+ */
+export const CloneCaseSchema = z.object({
+  name: z
+    .string()
+    .regex(/^[a-zA-Z0-9_-]+$/, 'Invalid case name format. Use only letters, numbers, hyphens, underscores.'),
+  repository: z.string().min(1).max(2048),
+  /** Branch or tag → `--branch <ref> --single-branch`. */
+  ref: z.string().min(1).max(200).optional(),
+  /** `--depth 1`. */
+  shallow: z.boolean().optional(),
+  description: z.string().max(1000).optional(),
+});
+
+/** Schema for POST /api/cases/clone-preflight — ask the remote what it has, clone nothing. */
+export const ClonePreflightSchema = z.object({
+  repository: z.string().min(1).max(2048),
+});
+
 const RemoteCommandOverridesSchema = z
   .object({
     shell: z.string().min(1).max(300).optional(),