dashboard: ZH/EN switcher — wire dynamic render strings (Stage C)

Extends I18N with ~70 more keys and routes every dynamic chrome string
through t(): KPI subtitles, daily-brief field labels (她的观点→Her view
etc.; bodies stay Chinese) + headers + meta bits, footer disclaimer,
theme-filter "all", the full stats panel (verdict templates via fragment
keys, tech line, CCF caption/axis, caveat, market β/α/residual line,
NA state), fundamentals labels + source/earnings/foreign, momentum
badges, concentration card + cluster warning, track-record card + badge,
detail strings (preview/pinned/samples/open-source), and all empty states.

Fix: renderBriefs' theme loop param `t` shadowed the i18n t(); captured it
as T before the map so the in-map label lookups resolve correctly (the
shadowing crashed briefs/track/detail render).

Verified: zh default renders all chrome Chinese + digest bodies Chinese;
EN flips KPIs/briefs/track/footer/stats/fundamentals to English while
authored digest/source content stays as written; round-trips; console
clean. Authored content (digests, cn_summary, source_text, tickers,
themes) untouched.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: lanfuli