Land staged session/MCP/chrome work + sidebar clear-J fix

This batches the in-flight [Unreleased] block from CHANGELOG.md into a
single commit. Highlights:

- Real MCP protocol layer (initialize / tools/list / tools/call) so
  vendor MCP clients can complete the handshake against the per-PID
  socket. Legacy direct-dispatch preserved for the harness.
- New mcp_injection kinds — cli_override for codex, config_env for
  opencode — joining the existing env-var and config_file paths so
  patterm can slot into more agents without touching their real
  config or auth.
- Ctrl+A/D and Ctrl+W/S focus navigation across tabs and intra-tab
  process lists, recognised in legacy / kitty CSI u / xterm
  modifyOtherKeys encodings.
- Palette macros (sw / k / sp ) and reordering so open sessions
  surface above spawn-new entries.
- Two-row tab bar, sidebar/tabbar/status chrome cache, viewport-wipe
  on agent spawn, CR-terminated orchestrator injections, and split-
  Enter PTY writes so paste-detecting TUIs see Enter as a key event.

Also fixes the bug logged in TODO: claude's Ctrl+O tool-call expansion
emits CSI 0 J, which the viewport renderer was forwarding verbatim —
wiping the sidebar to the right of the cursor and leaving the chrome
cache convinced nothing had changed. CSI 0 J and CSI 1 J are now
translated into per-row ECH sequences clamped to the viewport, same
as CSI 2 J and CSI K already were.

Agent guides (CLAUDE.md / AGENTS.md) now spell out the
TODO->CHANGELOG workflow so completed items land in the changelog
rather than as ticked entries left behind in TODO.

TODO.md

@@ -1,9 +1,2 @@
-- [ ] Killed agents are visible in the command palette. They shouldn't be.
-- [ ] claude failed to connect to patterm mcp -32601
-- [ ] codex doesn't show the patterm mcp at all
-- [ ] opencode doesn't show the patterm mcp at all
-- [ ] Open agents/processes should appear above the option to open a new one in the palette
-- [ ] Some sort of macros in the command pallete would be nice, like if i type `sw <query>` it would only show the switch entries. Maybe we should have info text greyed out to show these macros.
-  - [ ] sw <query> = switch
-  - [ ] k <query> = kill
-  - [ ] sp <query> = spawn
+- [ ] When the parent agent/orchestrator is killed, all child processes spawned by it should also be killed.
+  - [ ] This should apply to when we detect the process dies, like if the user Ctrl + C's out.