feat: inject effort as soft default via CLI flags instead of env var (#104)

CLAUDE_CODE_EFFORT_LEVEL hard-locks effort for the whole session and makes
Claude reject in-session /effort switching (incl. ultracode). Carry effort
as a dedicated payload field instead, injected at spawn as a soft default:

- regular levels (incl. max) -> claude --effort <level>
  (the settings effortLevel key is enum([low,medium,high,xhigh]) with
  .catch(undefined), so max would be silently dropped there)
- ultracode -> claude --settings '{"ultracode":true}'
  (dedicated boolean settings key, rejected by the --effort flag)

Changes:
- add effort enum field to create/quick-start/ralph-loop schemas and thread
  it through Session -> CreateSessionOptions/RespawnPaneOptions -> spawn
- buildEffortCliArgs() in session-cli-builder, shared by tmux spawn command
  and direct-PTY fallback args
- frontend: buildEnvOverrides() no longer emits CLAUDE_CODE_EFFORT_LEVEL;
  validated effort goes into payloads via getEffortSetting()
- settings UI: add Ultracode option to the Thinking Effort dropdown
- legacy migration: Session constructor extracts CLAUDE_CODE_EFFORT_LEVEL
  from persisted envOverrides; applyEnvOverrides() unsets the stale tmux
  session var so respawned panes are no longer locked
- tests: test/effort-injection.test.ts (13 cases)

Co-authored-by: Teigen <teigenzhang@gmail.com>

src/web/server.ts

@@ -1716,6 +1716,8 @@ export class WebServer extends EventEmitter {
             const recoveryClaudeMode = await this.getClaudeModeConfig();
             // Recover envOverrides from the internal __envOverrides field written by
             // session-manager (see updateSessionState). Cast to read the non-public field.
+            // Note: a legacy CLAUDE_CODE_EFFORT_LEVEL entry is auto-migrated to `effort`
+            // by the Session constructor (env var would hard-lock /effort switching).
             const savedEnvOverrides = (savedState as { __envOverrides?: Record<string, string> })?.__envOverrides;
             const session = new Session({
               id: muxSession.sessionId, // Preserve the original session ID
@@ -1728,6 +1730,7 @@ export class WebServer extends EventEmitter {
               claudeMode: recoveryClaudeMode.claudeMode,
               allowedTools: recoveryClaudeMode.allowedTools,
               envOverrides: savedEnvOverrides,
+              effort: savedState?.effort,
             });
 
             // Update session name if it was a "Restored:" placeholder or doesn't match saved name