feat: deliver Like activity to relays

[sinoru]

What

ReactionService now delivers Like and Undo Like ActivityPub activities to relay servers when the target note's visibility is public, matching the existing relay-delivery pattern in NoteCreateService, NoteDeleteService, PollService, NotePiningService, AccountUpdateService, and AccountMoveService.

A new admin meta option deliverReactionsToRelays (default true) is added so operators can opt out. The toggle is exposed under /admin/relays.

Closes #17307.

Why

Previously ReactionService delivered Like/Undo Like only to the note author (direct) and followers. RelayService was not injected at all, so reactions were never broadcast through relays — even though the notes themselves are. As a result, instances that pull notes via a relay could never see reactions on those notes, which weakens the social experience on smaller instances that rely on relays for content discovery.

Reactions occur far more frequently than note creations, so this PR also adds an admin opt-out. Operators concerned about amplification load on relays or downstream servers can disable the new behavior without affecting the existing direct/followers delivery.

Additional info (optional)

Scope

• Applies to Like / Undo Like only. Other under-relayed activities (e.g. Delete Person, account suspension) are intentionally out of scope.
• ActivityPub payload is unchanged — only the recipient set is extended — so no misskey-hub doc PR is needed.

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 25.01%. Comparing base (6229ac3) to head (8228434).
⚠️ Report is 13 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/backend/src/core/ReactionService.ts	20.00%	2 Missing and 2 partials ⚠️
...kend/src/server/api/endpoints/admin/update-meta.ts	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #17362      +/-   ##
===========================================
+ Coverage    24.70%   25.01%   +0.31%     
===========================================
  Files         1151     1155       +4     
  Lines        39093    39348     +255     
  Branches     10887    10932      +45     
===========================================
+ Hits          9659     9844     +185     
- Misses       23584    23647      +63     
- Partials      5850     5857       +7     

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[github-actions]

このPRによるapi.jsonの差分

差分はこちら

--- base
+++ head
@@ -9920,6 +9920,9 @@
                     "enableReactionsBuffering": {
                       "type": "boolean"
                     },
+                    "deliverReactionsToRelays": {
+                      "type": "boolean"
+                    },
                     "notesPerOneAd": {
                       "type": "number"
                     },
@@ -10221,6 +10224,7 @@
                     "perUserHomeTimelineCacheMax",
                     "perUserListTimelineCacheMax",
                     "enableReactionsBuffering",
+                    "deliverReactionsToRelays",
                     "notesPerOneAd",
                     "backgroundImageUrl",
                     "deeplAuthKey",
@@ -19364,6 +19368,9 @@
                   "enableReactionsBuffering": {
                     "type": "boolean"
                   },
+                  "deliverReactionsToRelays": {
+                    "type": "boolean"
+                  },
                   "notesPerOneAd": {
                     "type": "integer"
                   },

Get diff files from Workflow Page

[github-actions]

Backend memory usage comparison

Before GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	307.56 MB	297.56 MB	-9.99 MB	-3.25%
VmHWM	307.56 MB	297.56 MB	-9.99 MB	-3.25%
VmSize	23104.11 MB	23094.06 MB	-10.05 MB	-0.04%
VmData	1369.89 MB	1359.45 MB	-10.43 MB	-0.76%

After GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	307.57 MB	298.00 MB	-9.57 MB	-3.11%
VmHWM	307.57 MB	298.00 MB	-9.57 MB	-3.11%
VmSize	23104.36 MB	23094.48 MB	-9.88 MB	-0.04%
VmData	1370.14 MB	1359.86 MB	-10.27 MB	-0.74%

After Request

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	307.90 MB	298.38 MB	-9.51 MB	-3.09%
VmHWM	307.90 MB	298.38 MB	-9.51 MB	-3.09%
VmSize	23104.53 MB	23094.48 MB	-10.05 MB	-0.04%
VmData	1370.30 MB	1359.86 MB	-10.43 MB	-0.76%

See workflow logs for details