v0.3.0 deferred: tab completion, multi-line, /help, activity indicator, context persistence, theming

- Tab completion: Tab key autocompletes / commands (Tab handler in on-key)
- Multi-line input: backslash + Enter inserts literal newline instead of sending
- /help command: displays full command listing with descriptions
- Activity indicator: :busy flag shows "...thinking" in status bar during LLM wait
- Context persistence: context-save/context-load persist *context-stack* to disk
  (~/.cache/passepartout/context.lisp). Auto-restores on skill load.
  Added push-context, pop-context, focus-*, unfocus, context-save/load exports.
- Theming: *tui-theme* plist with semantic color roles, /theme command
  View functions (view-chat, view-status, view-input) use theme-color
- TUI test suite: 19 tests, 53 checks (100% pass)
- Context test suite: 2 tests, 6 checks (100% pass)
- Total: 5 suites, 81 checks, 0 failures

lisp/core-defpackage.lisp

@@ -38,10 +38,20 @@
    #:snapshot-memory
    #:rollback-memory
     #:context-get-system-logs
-    #:telemetry-track
     #:context-assemble-global-awareness
     #:context-awareness-assemble
     #:context-query
+   #:push-context
+   #:pop-context
+   #:current-context
+   #:current-scope
+   #:context-stack-depth
+   #:context-save
+   #:context-load
+   #:focus-project
+   #:focus-session
+   #:focus-memex
+   #:unfocus
    #:process-signal
    #:loop-process
     #:perceive-gate