feat(context): add tmux-context plugin injecting the agent's tmux location

Add @deepseek-ai/dsh-tmux-context: an opt-in per-turn context plugin that
reads which tmux session/window/pane this agent process runs in (plus the
window layout tree) via the ctx.bash seam, and injects it as one durable,
source-attributed user/message when the location changes.

- Pull on the first step of each turn; no tmux hook or background process.
- Detect a real pane by tty, not $TMUX_PANE alone: a terminal launched from
  a tmux shell inherits $TMUX/$TMUX_PANE from that ancestor, so the command
  also matches the pane's #{pane_tty} against this process's controlling
  terminal and emits fields only on a match.
- No-op outside a real pane, without a bash executor, or on a malformed
  reading.
- Own location and layout only: no pane sizes, no sibling-pane scraping.
- Unit tests at 100% per-file coverage, plus a keyless Loader e2e with a
  mock bash provider so it replays without tmux.
- Agent Note: 2026-07-27-tmux-location-context.

docs/config-catalog.md

@@ -1487,6 +1487,20 @@ export interface Config {
 
 Source: [`packages/context/time-context/src/index.ts:20`](../packages/context/time-context/src/index.ts)
 
+## `@deepseek-ai/dsh-tmux-context`
+
+Requires: `agents`
+
+```ts config-catalog
+/** Per-turn tmux-location scheduling. Invalid values fail plugin load. */
+export interface Config {
+  /** Minimum milliseconds between durable injections in one session. Omit or set to 0 to inject on every eligible change. */
+  refreshIntervalMs?: number
+}
+```
+
+Source: [`packages/context/tmux-context/src/index.ts:33`](../packages/context/tmux-context/src/index.ts)
+
 ## `@deepseek-ai/dsh-token-meter`
 
 ```ts config-catalog