AGENTS.md for repo

[tsrikris]

Summary

Governance and docs cleanup:

• AGENTS.md is now the single authoring contract, and CLAUDE.md collapses to
  a one-line pointer at it.
• Trace-collection guidance moves from the standalone collect-traces.md page
  into the two report docs readers already land on; the orphan page is removed.
• The Project Structure tree moves from CONTRIBUTING.md into README.md, corrected to match disk.

Changes

• AGENTS.md / CLAUDE.md. Rewrote AGENTS.md as a lean rules-of-engagement
  contract (change scope, reuse, correctness, hygiene); reduced CLAUDE.md to
  Read [AGENTS.md](AGENTS.md).
• Trace collection. Capture snippet and profiler-flags table now open
  generate-perf-report-pytorch.md as ## Collect a trace; the sanity-check
  list is now ## Before you trust a report in the inference report doc. Removed
  collect-traces.md and repointed every reference (README.md,
  docs/index.rst, docs/how-to/agent.md, Agent Analysis/README.md) at the
  new #collect-a-trace anchor.
• Project Structure tree. Moved to README.md, fixing the unclosed-fence bug
  and dead Black ToC entries in CONTRIBUTING.md. Added the missing Agent/,
  TraceIndex/, TraceUtils/, notebooks/, and scripts/ dirs; fixed the tree
  glyph and the GPUEventAnalyser spelling.

[kyle-hoffmeyer]

@tsrikris, I would also consider adding:

"When writing docstrings and code comments, follow surrounding code structure. Don't write unusually long code comments or docstrings"
"When creating utility functions, see if they already exist and reuse when possible. If they don't exist, think about where it should go."
"Keep imports at the top. The only exception is when imports are conditional"