post-restructure doc debt: broken links, inverted toolchain claims, stale consumer instructions

[lann]

Left behind by the rust/+js/ restructure (182f911) and subsequent growth:

• Five dead relative links: js/componentize/README.md:6 (../lann-webcrypto-guest), :52 (../examples/componentize-demo), :78 (workflow link), js/componentize/wpt/README.md (workflow link), examples/componentize-demo/README.md:5 (../../webcrypto-componentize).
• README.md:145-151 describes the two componentize checks' requirements backwards: wpt::test does not use a "published runner component" (the runner is componentized from the tree; the toolchain is downloaded, digest-verified — js/componentize/wpt/component.sh:6-14), and componentize::test does not "need the componentize-js CLI" (js/componentize/README.md:72-82: nobody here builds it; it downloads on first use).
• js/componentize/README.md:48-50 tells consumers their world "must import" 2 interfaces; the shim statically imports ~30 (js/componentize/webcrypto.js:156-196), so the prescribed world fails at componentize time. The file's own header carries the correct list.
• js/componentize/wpt/README.md's "What is vendored" table is missing the wrapKey_unwrapKey row (landed 0c39433).
• Minor: README.md:169 / AGENTS.md claim just ci mirrors CI exactly; CI additionally runs the macOS WebKit parity job pair. experiments/hpke/justfile:21 points at a _compose that moved to justfile.shared.just.

Related: #270 (another stale conformance README claim).