all: correctness, performance, and refactoring pass

[ryanccn]

Correctness

• purge charged its budget for messages requested rather than deleted, so a filtered-out message silently cost a slot; now paginates with a before cursor and charges only actual deletions.
• MessageUpdate wrote message content to Redis before checking the log exclusion list; the check now precedes the write.
• Message handlers run under join! instead of try_join!, so one failing handler can no longer cancel a code expansion between sending and recording it.
• Code expansion rejects inverted and out-of-bounds line ranges up front, and caps them at 256 lines.
• Safe Browsing never matched http:// URLs: scheme stripping fell through to the unstripped string, so every plain-HTTP hash was computed with the scheme still attached.
• Safe Browsing path expressions now follow the spec — anchored at the root with trailing slashes, capped at four — instead of suffix truncations that matched nothing the database stores.
• fullHashes:find may return a 4–32 byte hash prefix; matching it required an exact 32-byte hash, silently dropping those results.
• One unparseable URL no longer fails the scan for the whole message.
• The Rice decoder sized its buffer from an unbounded wire value, panicked on a zero prefix size, and accepted trailing partial prefixes.
• Safe Browsing update retries on checksum drift are bounded rather than looping forever.
• dedent computes a real common prefix, leaving mismatched indentation alone.
• A single failing guild no longer aborts the daily colour role rotation.

Performance

• Safe Browsing prefixes are packed into one sorted allocation and looked up by binary search, replacing a Vec<Vec<u8>> alongside a HashSet holding a second copy of every prefix — roughly 10 MB and 200k allocations per list down to 1.2 MB and two.
• Safe Browsing updates build the new prefix set from borrowed slices instead of deep-cloning the database, and checksum it without materialising a flattened copy.
• sha256 returns [u8; 32] rather than allocating, and URL checks no longer allocate a key string per hash.
• Autoreply patterns are compiled once per guild and cached, pruned to whatever the guild currently configures, instead of recompiling every pattern on every message.
• Message edit and delete logging fetch the guild config and run the exclusion check once instead of twice; bulk deletes fetch once for the batch rather than per message.
• Starboard deletion checks Redis before fetching the guild and channel, so an ordinary deletion costs no API calls.
• ThreatType no longer allocates a String per serialisation.
• Dropped rayon, now that the parallel scan it existed for is gone.
• Intelligence checks the mention prefix before looking up the member, and skips the lookup entirely when no role allowlist is configured.
• Starboard fetches the guild once per event instead of twice, and parses starboard_emojis once instead of once per reaction.
• utils::truncate borrows instead of allocating on every call.
• StorageKey builds one buffer instead of four allocations per key; wire format unchanged.
• Analytics events dispatch in the background instead of blocking message handling.
• Code expansion no longer materialises every fetched line to select a few.
• Dropped an HTTP call in DM logging that re-derived an already-known fact.

Refactoring

• ModerationAction replaces ~660 lines of duplicated scaffolding across ban, kick, timeout, purge_user, and warn, preserving the existing DM → log → action → reply ordering.
• Five near-identical code expansion handlers collapse into expand_file + render_snippet; resolve's eight capture loops become one macro.
• translate/translate_ephemeral and both code_expand commands share one implementation, differing only in how they defer.
• Five analytics::send_* wrappers become one send_event.
• log::is_excluded and is_excluded_message merge into one function taking an optional pre-fetched config.
• rotate_color_role returns Option<RoleId> rather than a HashSet that never held more than one element.
• The config interaction handler's ten match arms collapse to their differing assignments.
• Removed dead commented-out honeypot code, a single-element Vec, shadowed imports, option_env! for an always-present CARGO_PKG_VERSION, and a needless clone of message content.
• Safe Browsing prefix storage moves into a PrefixSet type, and update decoding into decode_removals and Additions.
• Tests cover the spec's suffix/prefix expression examples, prefix set lookups, Rice round trips, and the autoreply cache.