fix(bridge): pin the loopback token exemption to the extension's stable origin

[chintoleung]

Fixes #108

Problem

Any installed extension could bypass bearer-token auth by presenting its own chrome-extension:// Origin (prefix check in attach()).

Approach

• The exemption is now an exact-match allowlist (trustedExtensionOrigins); default is the shipped extension's id. Chromium derives an unpacked extension's id from the manifest key, so this PR pins a committed key → stable id ampcoeplakeelcoengijbfbhjnlbdign across machines and updates. Unlisted origins — including other extensions — must present the token; origin trust never applies off loopback.
• trustedExtensionOrigins entries are validated (chrome-extension://<32-char a-p id>) and the effective allowlist is logged at mount. [] is the explicit hardened mode (token pairing only) for hostile-extension or loopback-proxy (tailscale serve, ssh -L) topologies.
• Migration: updating from pre-0.1.5 changes the extension id once (settings are stored per id) — READMEs and both installers now tell users to re-enter a configured remote bridge address/token. Version bumped to 0.1.5.
• Drift guard: a test fails if the manifest key ever hashes to anything but the pinned id.

Boundary (documented)

The manifest key is public: the pin stops incidental cross-extension access, not deliberate key-cloning; origin checks bind browser contexts only. Hardened deployments set trustedExtensionOrigins: [] and pair the token.

Testing

• New unit tests: unlisted-origin rejection, trusted-origin + non-loopback rejection, explicit [] fail-closed, invalid config entries throw, key→id drift guard.
• e2e (real Chromium): asserts the loaded extension id is the pinned id and that a tokenless hello connects against the default allowlist; second case covers the paired-token path. Harness is now locale-independent and skips loudly.
• Suites: bridge 160/160, extension 398/398, typecheck clean.

Notes for review

• One 4-line comment conflict with fix(browser): connect remote --host 0.0.0.0 bridge clients #100 (index.ts config-route block) — resolution should keep this PR's wording; the wider connect-src in fix(browser): connect remote --host 0.0.0.0 bridge clients #100 does not weaken the allowlist (non-loopback always needs the token).
• Follow-up (not in this PR): a distinguishable WS close code for untrusted origins so the panel can render an actionable message.

中文摘要

回环免 token 从「任意 chrome-extension:// 前缀」改为精确 Origin 白名单：扩展固定 manifest key，id 在各机器与升级间稳定，默认仅信任该 id；其余 Origin 一律携带 token。配置项含格式校验与启动日志，[] 为加固模式。0.1.5 前版本升级时 id 会变更一次，需重新填写远程桥地址/token（README 与安装器已注明）。