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/public/index.html

@@ -1104,8 +1104,9 @@
                 <option value="high">High</option>
                 <option value="xhigh">XHigh</option>
                 <option value="max">Max</option>
+                <option value="ultracode">Ultracode (multi-agent workflows)</option>
               </select>
-              <span class="form-hint">Set CLAUDE_CODE_EFFORT_LEVEL for all new sessions (default = no override)</span>
+              <span class="form-hint">Default effort for new Claude sessions — soft default, switchable anytime in-session via /effort (e.g. /effort ultracode)</span>
             </div>
             <!-- Nice Priority Section -->
             <div class="form-section-header">Nice Priority</div>