docs(claude): refactor CLAUDE.md for higher signal-to-noise

[songkuan-zheng]

Summary

Restructure CLAUDE.md to surface the rules that matter and trim the
rules that don't. No safety rule was dropped — only consolidated,
demoted from emphasis, or removed if it described filesystem layout
that's inferable from `ls`.

• Hoist five safety-critical rules into a "Hot path" section at the
  top so Claude grep-anchors there first when reading the file.
• Add "Agent constraints (this fork)" — names actions Claude
  must not take autonomously (push to `ship`/`internal`, run
  `scripts/release-tag.sh`, edit upstream UI build artifacts).
• Add "Test discipline" — covers spec-first assertions,
  `pytest.mark.xfail(strict=True)` for known doc-vs-impl gaps
  (instead of `skip` / TODO), and the "test exposed a bug ≠ bug is
  fixed" PR-summary norm.

Mechanical cleanups:

• Collapse five command-list sections (Installation / Testing / Code
  Quality / Single Test Files / Running Scripts) into one
  "Development workflow" block.
• Compress the "Architecture Overview" enumeration of folders — what
  `litellm/main.py`, `litellm/llms/`, `litellm/proxy/auth/` etc.
  contain is inferable from the directory tree. Keep only non-obvious
  design decisions.
• Drop emphasis (bold / NEVER / MUST) on style preferences that
  don't cause production incidents (dict spread, comprehension
  extraction, FastAPI Query declarations). Emphasis remaining is
  reserved for rules whose violation has caused or could cause data
  loss, security holes, or production outages.

Numbers

	before	after	change
Words	2538	2000	-21%
Estimated tokens	~3300	~2600	-21%
Emphasis markers	38	9	-76%

Rule-preservation spot checks

All 13 verified preserved in the new file:
Never-raw-SQL · Prisma-model-methods · `LLMClientCache._remove_key` ·
`release-tag.sh` · `ship/v1.83.10` PR target · antd migration ·
`sessionStorage` · `schema.prisma` · `TRANSPORT.OPENAPI` · MCP
credential table · no-pipe-curl-to-shell · `check_valid_key` ·
`litellm-proxy-extras` migration lag.

Test plan

• Visual review of new section order
• Confirm no safety rule was lost vs the pre-refactor version
• Confirm emphasis is now reserved for incident-grade rules only