refactor(src): reorganize plaud_tools by surface (core/cli/mcp_pt/tray)

[massive-value]

Summary

Splits the flat src/plaud_tools/ file list into packages grouped by consumer, decided from actual import fan-in/fan-out rather than guesswork:

• core/ — shared domain layer (client, session, auth, transport, models, errors, appdata, layout, transcode, query, ai_clients) used by 2+ of cli/mcp/tray
• cli/ — cli.py, doctor.py, and process_probe.py (renamed from mcp_lifecycle.py — the old name outlived a prior dead-code removal that left only a doctor-only process-enumerator probe)
• mcp_pt/ — mcp.py, server.py (named mcp_pt, not mcp, to avoid shadowing the mcp SDK package these modules import)
• tray/ — unchanged, plus completions/, scripts/ (PS1 update/uninstall templates), and ps1_templates.py consolidated in since they're tray-exclusive by actual usage

assets/ and the repo-root /scripts/ stay put: assets/icon.ico is shared by both the mcp_pt and tray PyInstaller builds, and /scripts/install.ps1 is fetched by a public raw-GitHub URL baked into the README.

No behavior, CLI/MCP surface, or entry-point change — pure module reorg. Also updated:

• All relative/absolute imports across src/, tests/, scripts/
• pyproject.toml entry points + mypy overrides
• pyinstaller/*.spec hiddenimports and bundled-data paths
• CI/ADR comments referencing the renamed module
• Current-state docs (CLAUDE.md, CONTEXT.md, CONTRIBUTING.md)

Historical docs (CHANGELOG entries, ADRs, plan docs) were deliberately left untouched — they describe what was true when written.

Two bugs caught by the test suite during the move (both fixed here, not pre-existing):

1. ps1_templates.py's dev-mode path resolution broke when the file moved a directory deeper — fixed.
2. --diagnose-enum's error string changed text, which would have silently defeated a regression test checking for the old string — test updated to match.

Test plan

• pytest -q -m "not live" — 1027 passed
• ruff check src/ scripts/ tests/ — clean
• mypy src/plaud_tools — clean
• Reinstalled editable package (pip install -e . --no-deps) and verified all four console-script entry points (plaud-tools, pt, plaud-mcp, plaud-tray) resolve and report the correct version
• Verified scripts_dir() and the new assets/completions paths resolve correctly at runtime

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