feat(watch): show plan mode as its own session status

[pfriedrix]

• lcc start launches every session in plan mode, so active was true on both sides of the only line that matters — whether the agent has been approved to touch files. A row now reads ◈ plan until it is, and the marker going away is the useful half.
• Needs no new hook: Claude Code already puts permission_mode on PreToolUse, UserPromptSubmit and Stop. Verified against a real 2.1.223 session rather than inferred — watch_hooks.zig's payload fixture is now a captured payload, and Notification/SubagentStart/SessionEnd genuinely carry no mode, which is why the daemon holds the last one it was told.
• This does break the module header's rule that lcc reads no payload fields. There is no matcher that selects on permission mode, so the exception is contained instead of avoided: an absent or unrecognised value is a no-op, freezing the last mode rather than clearing it.

Review notes

• plan is projected at the point a status is reported, not applied as a transition — nothing fires when a plan is approved, so a state would put "which mode am I in" inside apply and "does this decay" inside decay. watch_status.present holds the precedence, and waiting outranks plan mode: the approval prompt at the end of a plan is a permission prompt.
• status gains "plan" as a value; no JSON key was renamed or dropped. A caller switching on active/idle sees plan for a planning session, which is the point.
• The running daemon is an older build and will not send the new field until it restarts — lcc open already flags that as outdated_build.