…LizardByte#5299)

(cherry picked from commit fdf1363)

…ted patch

Third round of fork improvements on top of the branding/CI work:

* docs/CHANGELOG-SolarFlare.md (145 lines). Fork-specific changelog
  separate from upstream's docs/changelog.md. Enumerates every fork
  change (config plumbing, branding, web UI, build script, docs,
  cherry-picked upstream commits) in the unreleased section. Cross-
  references docs/PORTING.md, docs/CONFIGURATION.md, README.md and
  PUSH-INSTRUCTIONS.md.

* scripts/cachyos-build.sh post-install verification. After the
  'Install + verification' step, the script now:
    1. Verifies the installed sunshine binary contains the fork
       banner ('Fork: SolarFlare') -- catches the case where a
       leftover upstream package overwrote the fork install.
    2. Writes a 5-key test config to /tmp, runs 'sunshine <conf>'
       for 1 second, and checks that all 5 fork keys appear in the
       parse log without any 'Unrecognized' warnings.
  Both checks are non-fatal warnings (so the script still succeeds
  if sunshine isn't on $PATH or the binary is older than the
  source), but they're loud enough that 'I just installed the
  fork and a key isn't taking effect' is now a clearly printed
  warning instead of a silent runtime surprise.
  Also updated the post-install Done banner to identify the binary
  as 'SolarFlare' and surface the 5 fork tunables (was 'Sunshine').

* Regenerated cachyos-fastpath.patch against upstream base commit
  1fce18d, including the cumulative fork changes (config keys,
  branding macro). Was 420 lines / 7 files / +280/-2; now 569 lines
  / 7 files / +379/-2. Verified to apply cleanly to a fresh clone
  of LizardByte/Sunshine HEAD with 3-way merge for upstream's own
  changes to pipewire.cpp / stream.cpp since the fork base.

* PUSH-INSTRUCTIONS.md updated to:
    - Reflect the new patch stats (+379/-2, was +280/-2).
    - Show the regeneration command for both the cumulative patch
      (git diff 1fce18d..HEAD) and the historical patch
      (git diff 1fce18d..bbcd69b -> cachyos-fastpath-historical.patch).
    - Document the 3-way merge caveat for pipewire.cpp / stream.cpp.
    - Cross-reference docs/CHANGELOG-SolarFlare.md.

* Also cherry-picked in this batch (already committed locally):
    - 838aa57 build(deps): fix building on Linux with DRM capture disabled (LizardByte#5224)
    - 56d5936 feat(linux/xdgportal): Add support for pipewire-serial (LizardByte#5060)
    - eebb1b0 feat(linux/kwin): log object serial when available on stream creation (LizardByte#5299)
    - 69a2db2 fix(crypto): OpenSSL 4.x compatibility (LizardByte#5330)
  All four were verified to not touch any fork-modified file, so
  cherry-pick was conflict-free.

Verification:
* cmake --build build: success (incremental).
* ./build/tests/test_sunshine: 334 tests, 329 passed (was 328; the
  new upstream test_crypto.cpp added 1 test), 5 pre-existing skipped,
  0 failed. Exit 0.
* bash -n scripts/cachyos-build.sh: OK (post-install verification
  block has valid shell syntax).
* git apply --check cachyos-fastpath.patch on a fresh clone of
  LizardByte/Sunshine HEAD: applies cleanly (0 errors).
* Dependabot: 0 open alerts (still clean from round 2).