feat(telemetry): bound project volume sampling

[John-Ryan21337]

Summary

• coalesce concurrent reads for the same project root
• bound simultaneous helpers and cached roots
• cache successful samples from operation completion
• apply a bounded retry cooldown only after the underlying operation fails
• invalidate stale state safely after a monotonic-clock rollback
• keep telemetry for different roots isolated

Adoption order

Apply direct Cafe PR #15, then #37, then #38, then this PR. This branch contains those exact ancestor heads plus one unique commit. The unique delta is two new server files.

This PR adds only the bounded sampler. It does not add aggregation, RPC, Web UI, or temperature sensors.

Verification

• unique delta: 2 files, +520 lines
• focused sampler tests: 11 passed
• full typecheck: 9/9 packages
• exact-file lint passed without warnings
• exact-file format passed
• git diff --check passed
• production sampler blob exactly matches audited source commit 86e605e3

The test port also hoists one schema decoder to satisfy Cafe's current lint rule. It does not change behavior.