feat(commands): /compact alias + preview flags for /compress (#3243 salvage)

[teknium1]

Summary

Salvage of #3243 by @Mibayy — adds /compact as a first-class alias of /compress plus --preview/--dry-run flags on both the CLI and gateway surfaces; reimplemented against current main because the original diff targeted a removed gateway/run.py handler.

Changes

• hermes_cli/commands.py — compress CommandDef gains aliases=("compact",); args_hint/description document the new flags. /compact now resolves everywhere (CLI, gateway, Telegram/Slack/Discord command lists, autocomplete) — and fixes the dangling /compact references in main's context-exhausted error banners (gateway/run.py:2513, :11707).
• hermes_cli/partial_compress.py — new pure helpers shared by both surfaces: extract_compress_flags() (strips --preview/--dry-run/--aggressive so they coexist with the existing here [N] / --keep N / focus-topic args) and summarize_compress_preview() (message counts, token estimate, here boundary — side-effect-free).
• cli.py _manual_compress — --preview/--dry-run print the report and return without compressing; --aggressive prints an explanatory redirect (see below).
• gateway/slash_commands.py _handle_compress_command — same semantics; the preview path returns before any AIAgent construction or transcript write (no provider/API key needed).
• locales/*.yaml — gateway.compress.aggressive_unsupported added to all 16 catalogs (parity test enforced).
• scripts/release.py — AUTHOR_MAP entry for contributor credit.
• Tests — tests/cli/test_compress_flags.py (17 tests: alias resolution, flag extraction, preview report shape/purity) and tests/gateway/test_compress_preview.py (7 async tests: preview/dry-run/aggressive paths assert rewrite_transcript/update_session are never called).

Dropped: --aggressive (deliberately)

The original PR's --aggressive path called session_store.rewrite_transcript directly to hard-truncate to the last 4 messages. On current main that's exactly the pattern that caused the #44794/#39704 permanent-data-loss class — manual transcript rewrites outside the guarded _compress_context rotation/persistence machinery (rotation vs. in-place vs. failed-rotation handling, session repointing ordering, soft-delete audit trail). Implementing it safely would mean a parallel persistence branch on both surfaces; /compress here [N] and /undo already cover the use case. Instead of silently mis-parsing --aggressive as a focus topic, both surfaces recognize the flag and return an explanatory message pointing at those alternatives (--aggressive --dry-run still shows the preview plus the note).

Validation

Check	Result
scripts/run_tests.sh tests/cli/test_compress_flags.py tests/cli/test_partial_compress.py tests/gateway/test_compress_preview.py tests/gateway/test_compress_command.py tests/agent/test_i18n.py tests/hermes_cli/test_commands.py -q	259 passed, 0 failed
scripts/run_tests.sh tests/gateway/test_gateway_command_help.py tests/gateway/test_gateway_command_line_matcher.py tests/gateway/test_discord_slash_commands.py -q (alias slot/parity)	225 passed, 0 failed
ruff check on all touched files	All checks passed
Locale key parity (aggressive_unsupported in all 16 catalogs)	✅

Infographic

Closes #3243
Closes #3240

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