feat(reddit): add Reddit connector with comment sync and OAuth reply

[MaximeGaudin]

Summary

• Adds a Reddit connector (void-reddit) that polls configured subreddits and filters posts by keywords and minimum score (Hacker News pattern).
• Read-only mode uses application-only OAuth (client_credentials) with client_id + client_secret.
• Commenting mode (optional) runs a browser OAuth authorization_code flow during void setup, stores a refresh_token, syncs post threads with comments, and supports void reply / void send --via reddit.
• OAuth setup tries a loopback callback on localhost:8765 first; falls back to manual code paste when the port is busy, the browser cannot open, or setup runs on a remote machine.
• Runtime tuning via void reddit config|subreddits|keywords|min-score without editing config.toml.
• Plugin registry (refactor: connector plugin registry to eliminate parallel connector conflicts #30): Reddit registers via inventory::submit! in crates/void-cli/src/connectors/reddit.rs — no central ConnectorType enum or ConnectionSettings match arms. Settings are a generic TOML table on [[connections]].

Architecture

• Feed view: one channel conversation per subreddit (r/{name}); matching posts appear as messages.
• Thread view (when refresh_token is set): each matching post becomes a Thread conversation with comments as flat messages (metadata.parent_id for tree reconstruction).
• Reply IDs: conv:msg format via ReplyIdStyle::ConvMsg (same as LinkedIn/Slack).

Config example

[[connections]]
id = "reddit"
type = "reddit"
client_id = "your-reddit-app-client-id"
client_secret = "your-reddit-app-client-secret"
refresh_token = "stored-by-setup-when-commenting-enabled"  # optional
subreddits = ["rust", "programming"]
keywords = ["ai", "llm"]
min_score = 50

[sync]
reddit_poll_interval_secs = 3600

Register a web app at https://www.reddit.com/prefs/apps with redirect URI http://localhost:8765.

Usage

void setup                              # add Reddit; optionally enable commenting
void reddit subreddits add "rust"
void reddit keywords add "ai,llm"
void reddit min-score 50
void sync --daemon
void reply <message-id> --message "Thanks!"
void send --via reddit --to <post-id> --message "Great post!"

Test plan

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace
• API: client_credentials + refresh_token grants, comment tree parsing, post_comment (wiremock)
• Sync: filter logic, thread/message builders, comment metadata
• Config: refresh_token parsing, secret redaction, backward compat without refresh_token
• CLI: void reddit commands, Reddit build_reply_id conv:msg format
• OAuth setup: callback parsing, state validation, manual code extraction
• Registry: Reddit plugin validation, build via by_id("reddit"), badge RD