Add wt-perf timeline subcommand for trace capture & rendering

[max-sixty]

Summary

Adds wt-perf timeline to standardize how we capture and read traces for one-off wt invocations (alias dispatch, wt list, etc.). Replaces the prior RUST_LOG=debug wt … 2>&1 | wt-perf trace > trace.json dance with a single command that runs wt, captures stderr, parses [wt-trace] records, and either pretty-prints a sorted text timeline or emits Chrome Trace Format JSON for Perfetto.

The text mode is the path I expect to use most — it's a column-aligned table sorted by start time, with subprocess totals and an externally-measured wall (spawn → wait) so the unobserved prelude/epilogue is visible:

ts(ms)  dur       tid  kind  name
0.000   11µs      1    span  init_logging
0.043   3.979ms   1    span  prewarm
0.058   3.882ms   1    cmd   git rev-parse --git-common-dir … HEAD [wt-perf-typical-1]
…

3 subprocesses totaling 11.315ms (slowest: 3.882ms git rev-parse … HEAD)
traced: 14.838ms (first → last [wt-trace] record)
wall:   19.367ms (spawn → wait; +4.529ms untraced prelude/epilogue)

What's in the diff

• tests/helpers/wt-perf/src/main.rs — new Timeline subcommand. Resolves wt as a sibling of current_exe() (Windows-aware via EXE_SUFFIX), optionally invalidates caches with --cold [--repo PATH], runs wt with RUST_LOG=debug, captures stderr, and renders. Uses tabwriter for column alignment, Duration's std Debug for compact unit display, and insta for inline snapshot tests.
• tests/helpers/wt-perf/Cargo.toml — new deps: tabwriter (release), insta (dev).
• CLAUDE.md — fixes stale --skip syntax in the Benchmarks section (Criterion takes a positional FILTER, per docs(bench): replace --skip with positional FILTER #2547), replaces the non-existent bench_list_by_worktree_count example, adds a Traces section.
• benches/CLAUDE.md — leads "Generating traces" with wt-perf timeline; the manual stderr-redirect pipeline is now framed as the path for traces from a log already on disk.
• src/trace/mod.rs module doc — same usage block update so library doc and CLAUDE.md don't drift.
• wt-perf setup printed suggestion — hints at wt-perf timeline instead of the manual stderr redirect.

wt-perf trace (stdin/file → Chrome JSON) and wt-perf cache-check are unchanged — they still serve the case where you have a captured log and want to convert or analyze it without re-running.

Test plan

• cargo run -- hook pre-merge --yes (3432 tests, lints, doctests) passes locally
• wt-perf timeline -- -C \$REPO stub end-to-end on a typical-1 fixture
• wt-perf timeline --cold --repo \$REPO -- -C \$REPO stub invalidates and reruns
• wt-perf timeline --chrome -- -C \$REPO stub produces valid JSON (loaded into python -m json.tool)
• cargo test -p wt-perf --bin wt-perf — 2 inline insta snapshots pass
• CI green

🤖 Generated with Claude Code

[worktrunk-bot]

One stale-comment nit inline. Separately: this PR fixes the --skip syntax in CLAUDE.md, but benches/list.rs:20-21 still shows cargo bench --bench list -- --skip cold / --skip real in its header comment — that's the same broken syntax (#2547). Worth folding into the same PR so the bench file's own examples agree with the doc this PR rewrites.