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.

internal/app/keymatch.go

@@ -142,3 +142,37 @@ func isModifyOtherKeysCtrlK(params string) bool {
 	}
 	return parts[0] == "27" && parts[1] == "5" && parts[2] == "107"
 }
+
+// matchCtrlChar reports whether chunk[i:] starts with Ctrl+<ch> where
+// ch is a lowercase ASCII letter. Recognises the same three encodings
+// as matchCtrlK: legacy single byte (Ctrl-A = 0x01 .. Ctrl-Z = 0x1A),
+// kitty CSI u with mods=5, and xterm modifyOtherKeys CSI 27;5;<key>~.
+// Only unmodified Ctrl (no Shift/Alt/Meta) and a press event match.
+func matchCtrlChar(chunk []byte, i int, ch byte) (matched bool, advance int) {
+	if i >= len(chunk) || ch < 'a' || ch > 'z' {
+		return false, 0
+	}
+	legacy := ch - 'a' + 1
+	if chunk[i] == legacy {
+		return true, 1
+	}
+	n := csiLen(chunk, i)
+	if n == 0 {
+		return false, 0
+	}
+	final := chunk[i+n-1]
+	params := string(chunk[i+2 : i+n-1])
+	switch final {
+	case 'u':
+		k, ok := decodeCSIu(params)
+		if ok && k.key == int(ch) && k.mods == 5 && k.event == 1 {
+			return true, n
+		}
+	case '~':
+		parts := strings.Split(params, ";")
+		if len(parts) == 3 && parts[0] == "27" && parts[1] == "5" && parts[2] == strconv.Itoa(int(ch)) {
+			return true, n
+		}
+	}
+	return false, 0
+}