Fix review drift: exceptions, model defaults, dead code, stale docs

[joy-void-joy]

Summary

Cleanup pass resolving drift found in review:

• Exception handling — narrow broad except Exception handlers to specific types and annotate the intentionally-broad guards with justifications
• Model defaults — default every model choice (background agents, observer, reviewer, docs/examples) to claude-opus-4-6
• MCP typing — replace Any-typed MCP plumbing with McpServerConfig/SdkMcpTool, key servers by name, generate tool docs from SDK tool definitions instead of getattr duck-typing
• Dead code — remove the unused charts module, session-listing/timestamp helpers, logs_path setting, and construction-only tests
• Docs — fix stale lup.lib.* module paths, README devtools listing, CLAUDE.md structure drift; drop the PLAN.md convention
• Devtools — TTY-aware usage watch mode, sh-based clipboard, ship py.typed in the lup package

Commits

• chore: gitignore .lup runtime directory
• chore(lup): ship py.typed marker
• refactor(lup): remove unused session-listing helpers
• refactor(lup): remove unused timestamp helpers
• refactor: tighten broad exception handlers
• fix: default all model choices to claude-opus-4-6
• fix(agent): key MCP servers by name in get_mcp_servers
• refactor(agent): generate tool docs from SDK tool definitions
• fix(devtools): disable usage watch mode outside a terminal
• refactor(devtools): replace subprocess clipboard with sh
• refactor(devtools): remove unused charts module
• refactor(agent): remove unused logs_path setting
• test: remove construction tests
• docs: fix stale module paths in docstrings
• docs(readme): fix devtools listing and truncated commands
• meta: drop PLAN.md convention
• meta(claude-md): align docs with actual code structure
• meta(commands): delegate fb-investigate trace reading to trace-explorer

Test plan

• uv run lup-devtools dev check — ruff format, ruff check, pyright, pytest all pass
• Rebuilt tree verified byte-identical to the pre-rebase merge result