perf: drop the cache layers that measured at zero

Ablation (PHASE2-FINDINGS.md) attributed the memory win to the
serverExternalPackages line and the integrations barrel diet. These three
measured at exactly zero and were most of the file churn, so they go:

next-cache-handler: orphaned. cacheHandlers and cacheComponents are both
already gone from next.config.ts and nothing imported the package — it
was reachable only through a stale dependency entry.

cache-tags / cache-invalidation: there is no "use cache", cacheTag,
cacheLife or unstable_cache anywhere in app source, so revalidateTag was
firing on tags nothing registers, with no handler to receive them, inside
a catch that swallowed the resulting out-of-scope error. Removing the
calls also removed the SELECTs that existed only to supply a board name
or member list to them, so board.ts, group.ts, user.ts, serverSettings.ts,
section-router.ts and change-search-preferences.ts return to the
merge-base exactly. The live in-process integration data cache is
untouched.

Redis 6 -> 2 client consolidation: no measurable effect at idle (139.3 vs
139.2 MiB) or under load. Reverted, but the pubSub:last:* TTL is kept —
that one is an unbounded-growth fix, not a consolidation.

23 files, -883 lines. Diff vs merge-base: 100 files/3336 insertions ->
82 files/2484. pnpm test 144/144 files, 1795 tests, 0 failures;
typecheck and lint clean; app and Docker image build.

pnpm-lock.yaml

@@ -860,9 +860,6 @@ importers:
       '@homarr/modals-collection':
         specifier: workspace:^0.1.0
         version: link:../../packages/modals-collection
-      '@homarr/next-cache-handler':
-        specifier: workspace:^0.1.0
-        version: link:../../packages/next-cache-handler
       '@homarr/notifications':
         specifier: workspace:^0.1.0
         version: link:../../packages/notifications
@@ -2087,25 +2084,6 @@ importers:
         specifier: 'catalog:'
         version: 7.0.2
 
-  packages/next-cache-handler:
-    dependencies:
-      ioredis:
-        specifier: 'catalog:'
-        version: 5.11.1(supports-color@10.2.2)
-      next:
-        specifier: 'catalog:'
-        version: 16.3.0-preview.9(@babel/core@7.29.0(supports-color@10.2.2))(@opentelemetry/api@1.9.0)(@playwright/test@1.61.1)(@types/node@24.13.3)(babel-plugin-react-compiler@1.0.0)(react-dom@19.2.7(react@19.2.7))(react@19.2.7)(sass@1.101.0)
-    devDependencies:
-      '@homarr/tsconfig':
-        specifier: workspace:*
-        version: link:../../tooling/typescript
-      typescript:
-        specifier: 'catalog:'
-        version: 7.0.2
-      vitest:
-        specifier: 'catalog:'
-        version: 4.1.10(@opentelemetry/api@1.9.0)(@types/node@24.13.3)(@vitest/coverage-v8@4.1.10)(@vitest/ui@4.1.10)(jsdom@29.1.1(@noble/hashes@2.0.1))(msw@2.14.6(@types/node@24.13.3)(typescript@7.0.2))(vite@8.1.4(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.101.0)(sugarss@5.0.0(postcss@8.5.16))(terser@5.46.1)(tsx@4.21.0)(yaml@2.9.0))
-
   packages/notifications:
     dependencies:
       '@homarr/ui':
@@ -21948,6 +21926,7 @@ snapshots:
     optionalDependencies:
       msw: 2.14.6(@types/node@24.13.3)(typescript@7.0.2)
       vite: 8.1.4(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.101.0)(sugarss@5.0.0(postcss@8.5.16))(terser@5.46.1)(tsx@4.21.0)(yaml@2.9.0)
+    optional: true
 
   '@vitest/pretty-format@4.1.10':
     dependencies:
@@ -29824,6 +29803,7 @@ snapshots:
       terser: 5.46.1
       tsx: 4.21.0
       yaml: 2.9.0
+    optional: true
 
   vitest@4.1.10(@opentelemetry/api@1.9.0)(@types/node@24.13.3)(@vitest/coverage-v8@4.1.10)(@vitest/ui@4.1.10)(jsdom@29.1.1(@noble/hashes@2.0.1))(msw@2.14.6(@types/node@24.13.3)(typescript@7.0.2))(vite@8.1.4(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.101.0)(sugarss@5.0.0(postcss@8.5.16))(terser@5.46.1)(tsx@4.20.4)(yaml@2.9.0)):
     dependencies:
@@ -29886,6 +29866,7 @@ snapshots:
       jsdom: 29.1.1(@noble/hashes@2.0.1)
     transitivePeerDependencies:
       - msw
+    optional: true
 
   vue-component-type-helpers@3.3.4: {}