feat(connector): Support GitHub

[xxx7xxxx]

Summary

• Add GitHub connector support through backend APIs, storage, OAuth handling, and access-log redaction.
• Add web connector models, controller, API client, and composer UI for attaching GitHub context.

Notes

• GitHub CSGHub App: apps/csgclaw
• CSGClaw currently does not have a public OAuth2 broker, so users need to configure their own GitHub OAuth credentials:

export CSGCLAW_GITHUB_OAUTH_CLIENT_ID='Iv23li1ng4Uy8VDAtpmI'
export CSGCLAW_GITHUB_OAUTH_CLIENT_SECRET='<client_secret>'

• Developers can ask me for the client secret.
• Currently, agents aren't aware of connector info (Will do it for the manager in the next contribution).

Screenshots

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