feat: add Reddit connector (saved + upvoted)

[graydawnc]

Summary

Adds @spool-lab/connector-reddit as a new plugin exporting two connectors:

• reddit-saved — posts and comments you saved on Reddit
• reddit-upvoted — posts you upvoted on Reddit

Both are persistent (ephemeral: false) user-owned lists.

Approach

• Auth: cookies:chrome — reuses the user's logged-in Reddit session. Same pattern as twitter-bookmarks / xiaohongshu.
• API: hits old.reddit.com's JSON API. Old Reddit accepts the reddit_session cookie directly — no OAuth bearer token needed.
• Username: resolved once via /api/me.json and cached per connector instance.
• Pagination: native Reddit after cursor, 100 items/page.
• Items: maps both t3 (posts) and t1 (comments) kinds. Filters Reddit's thumbnail sentinel strings (self, default, nsfw, etc.).
• Errors: 429/5xx with exponential backoff, 401/403 → AUTH_SESSION_EXPIRED (invalidates cached session).
• Forward-sync: stops at sinceItemId anchor, consistent with github-stars.

Capabilities declared

fetch, cookies:chrome, log — matches twitter-bookmarks.

Distribution

Not bundled — users install via spool://connector/install/@spool-lab/connector-reddit or the connectors directory. Added to packages/landing/public/registry.json.

Known limitations / follow-ups

• Retry/error-handling block in src/fetch.ts is structurally identical to twitter-bookmarks' graphql-fetch.ts. With two copies now, it's probably time to promote a shared fetchJsonWithRetry helper into @spool/connector-sdk. Deliberately left out of this PR to keep scope tight — will do as a refactor once a third consumer appears or in its own PR.
• Saved/upvoted is not exhaustive — Reddit also exposes hidden posts, submitted history, and comment karma feeds. Can add later if wanted.
• No unit tests in the package yet. Local smoke test (fake fetch over fixture listing covering t3/t1/sentinel-thumbnail/unknown-kind) passes — kept it in /tmp rather than adding a test harness to the package since no other connector package has tests either.

Test plan

• pnpm --filter @spool-lab/connector-reddit build — clean tsc
• pnpm build — full workspace turbo build passes
• Local smoke test against fixture listing response
• Manual: install via dev flow, verify checkAuth returns ok when logged in, sync pulls saved/upvoted pages
• Manual: log out of reddit.com, verify checkAuth returns AUTH_NOT_LOGGED_IN

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