feat(voyage): sync browser-side anchor-parser regex with Node-side allowlist
Step 16 of v4.3 playground plan. Mirror lib/parsers/anchor-parser.mjs
ANCHOR_LINE_RE + ATTR_RE + ID_RE constants verbatim into voyage-playground.html
inline-script (file COLON COLON scheme compat — no ES-module). parseAnchor(line)
validates id matches ANN-NNNN, target non-empty, line positive integer,
snippet ≤80c, intent in {fix,change,question,block}.
Trace: SC6, research/02 Sec T4, plan-critic blocker B4 + scope-guardian DEP-3.
Cross-file regex sync verified by static-grep test.