🐛 Fix Claude permission mode drift between session state and web UI

[Robdel12]

Summary

• The web UI was using approvalPolicy (Codex concept: ask/auto-edit/auto-full) to display Claude's permission mode pill, instead of the actual permission_mode (default/plan/acceptEdits/bypassPermissions/dontAsk) that the server already emits
• When Claude entered plan mode during a live session, the status pill would still show the old approval policy value — users couldn't tell which mode was actually active
• The server contract was already correct (emits permission_mode in both REST SessionState and WS SessionDelta), but the web frontend never consumed it

Changes

• stores/sessions.js — Add permission_mode to handleSessionDelta so WS delta updates flow into the session store
• pages/session.jsx — Replace approvalPolicy local state with permissionMode seeded from selected.value?.permission_mode (updated via store deltas); PATCH /api/sessions/:id/config now sends permission_mode instead of approval_policy
• components/input/message-composer.jsx — Status pill now renders Claude permission modes with correct labels (Plan Mode, Default, Accept Edits, Bypass, Don't Ask) and cycles through real modes on click
• components/input/provider-controls.jsx — ClaudePermissionPicker options updated to match real Claude permission modes
• tests/stores/sessions.test.js — 4 new tests covering permission_mode delta application, null-clear, preservation when absent, and resume propagation

What didn't change

• No server changes — the server already models permission_mode correctly through the connector event system, persistence, and broadcasts
• No native (Swift) changes — the Swift client already uses permissionMode throughout (reducer, store events, ClaudePermissionPill UI)

Test plan

• All 85 web unit tests pass (including 4 new permission_mode tests)
• Lint passes on all changed files (0 new errors)
• Manual: start a Claude session, enter plan mode → verify the status pill updates to "Plan Mode"
• Manual: exit plan mode → verify the pill returns to the correct active mode
• Manual: reconnect/resume a session → verify the pill shows the correct current mode

Closes #135