Add optional Letta memory integration for cross-session recall

[shranchi0]

Summary

• Adds an opt-in session memory feature powered by Letta that records session lifecycle events and lets users query past context via natural language
• Completely optional — the feature is inert when letta-client is not installed, and dormant when installed but not enabled
• Install with pip install tame[memory], then toggle on via command palette (y)

How it works

• Toggle Memory (y in command palette): First use shows an onboarding dialog explaining the feature. Subsequent uses toggle on/off instantly.
• Ask Memory (a in command palette): Opens a dialog where you can ask questions like "what fixed the timeout error?" — the Letta agent searches its archival memory of past session events
• Clear Memory (j in command palette): Wipes all stored session memory (with confirmation)
• Status bar shows [Memory: On], [Memory: Off], or [Memory: ⚠] when letta-client is installed

What gets recorded (when enabled)

• Session created (name, working directory, timestamp)
• Session ended (exit code, duration)
• Errors detected by pattern matcher
• Status changes (state transitions)

Architecture

tame/integrations/
└── letta/
    ├── __init__.py
    ├── client.py      # Thin wrapper around Letta SDK
    ├── bridge.py      # Event bridge (fire-and-forget async)
    └── prompts.py     # Agent persona/system prompt

Files changed

• New: tame/integrations/letta/ — client, bridge, prompts
• New: tame/ui/widgets/memory_dialogs.py — enable, recall, clear modals
• Modified: tame/app.py — conditional bridge init, lifecycle hooks, 3 actions
• Modified: tame/ui/widgets/command_palette.py — y/a/j entries
• Modified: tame/ui/widgets/status_bar.py — memory indicator
• Modified: tame/config/defaults.py — [letta] config section
• Modified: pyproject.toml — memory optional extra

Test plan

• ruff check passes
• ruff format --check passes
• All 268 tests pass (no letta-client installed — feature stays inert)
• Manual: install letta-client, run letta server, toggle memory on, create/kill sessions, use "Ask Memory"
• Manual: verify existing functionality is completely unaffected without letta-client