feat: consolidate browser skills and client integrations

[TristanIsK]

Problem and result

Browser Skills, client manifests and submission references were split between the CLI repository, local delivery folders and separate review branches. This change provides one source index and reproducible candidate-package builds in browser-cli-rs.

• Keep skills/lexmount-browser and its default ZIP unchanged; add skills/lexmount-browser-mcp for remote MCP instructions and host-managed OAuth.
• Centralize existing Codex CLI/MCP and Claude Code manifest templates under plugins/, with one shared icon. Build complete plugin ZIPs from canonical Skills instead of checking in client-specific Skill copies. New package versions are development candidates, not replacements for published versions.
• Add an integration index with sources, package commands, review/market links, OAuth dependencies and publication boundaries for WorkBuddy, Codex, OpenClaw, Hermes, Claude Code, Doubao, Qianwen and DeepSeek Harness.
• Preserve OpenClaw's independent security review in fix: harden OpenClaw plugin installation and security disclosure #33 and Linux Skill work in feat: support Linux in Browser skill #27; link their actual sources rather than duplicating pending changes. No deployed service, local installation or marketplace entry is modified.

Validation

• Offline package checks passed locally: all three profiles, shared Skill byte equality, deterministic rebuilds, SHA-256 sidecars, ZIP integrity, manifest/resource paths, CLI/MCP separation and symlink rejection.
• Original default CLI Skill ZIP is byte-for-byte identical to the pre-change output with the same source files.
• Both Skills pass Skill validation; generated Codex CLI and MCP plugins pass plugin validation; shell syntax and git diff --check pass.
• Add package CI on Linux, macOS and Windows; this validates packaging, not browser/client compatibility. Rust runtime is unchanged; the existing Rust CI remains intact.

MCP and Claude candidates still require real host acceptance before publication. The MCP instructions track the pending backend handoff contract; this PR does not merge or deploy its dependencies. Previously submitted packages remain unchanged.