LTR-18 Update Chrome and Firefox extensions for tags

[CountableNewt]

Summary

• move canonical bookmark tag parsing and validation into latr-web-client
• add accessible save-time tags to the Chrome and Firefox popup flows
• preserve authored tags across hosted OAuth continuation and failed-save retries
• send tagged quick saves through the current link.latr.bookmarks.saveBookmark contract
• handle Chrome MV3 action and Firefox MV2 browserAction popup behavior explicitly
• repin latr-packages to the publication manifest containing the current tag Lexicons
• build both browser targets from the shared WXT extension and document the target-specific artifacts
• replace flat-blue placeholder icons with the canonical transparent L@tr.link mark and explicitly map toolbar icons

Why

The browser extension had fallen behind the current community bookmark tag contract and published Lexicons. It also dropped tag intent during OAuth continuation, assumed the MV3 popup namespace in Firefox, and packaged placeholder artwork instead of the product icon.

Verification

• full scripts/ci.sh passed with Xcode beta selected
• extension typecheck passed
• all 16 extension tests passed
• credentialed Development Chrome MV3 build passed
• credentialed Development Firefox MV2 build passed
• generated manifests contain the expected MV3/MV2 popup and icon mappings
• generated browser assets are byte-identical to the corrected transparent source icons
• authoritative PDS serves the current listTags, setTags, renameTag, and deleteTag Lexicons
• no credentials or local environment files are included in this PR

Remaining risk

• unpacked authenticated browser QA is still pending: Chrome was not running and Firefox is not installed on the test Mac
• no Chrome Web Store, AMO, or Production submission is included
• the separate setState verb/OpenAPI drift remains tracked in LTR-19

Tracking

• LTR-18
• Related: LTR-13, LTR-15, LTR-19, LTR-20

[linear-code]

LTR-18