Add the qa gate: dev for speed, qa for proof

dev -> qa -> main, across every public repo.

dev is where work lands and is meant to be pushed to often, so ci.yml stays
the fast answer: fmt, clippy, unit tests, leak-guard. qa is the release
candidate, and qa.yml is the claim that a commit is production worth —
release-profile tests on all three platforms, and the Linux cross-target
clippy that the local precommit gate has always run but CI never did.

Release profile matters as its own gate: overflow checks are off, debug_assert
is compiled out, and inlining changes what the optimiser can prove. A test
that only passes in debug never guarded the binary anyone ships.

qa.yml checks siblings out at qa rather than dev. This is not a monorepo, and
a qa run resolving its dependencies from unreleased dev tips would go green on
a combination that is not the one shipping — the exact mismatch the branch
model exists to prevent. ci.yml now tracks whichever branch triggered it for
the same reason, since it also fires on qa.

The consequence is that repos move to qa together, in dependency order. qa is
backfilled from main so an unchanged crate still presents working code to the
crates built on it.

.github/workflows/ci.yml

@@ -2,10 +2,12 @@ name: CI
 
 on:
   push:
-    # `dev` is where work lands and where CI must be green. `main` only ever
-    # moves at release time, to the tagged commit, so a push to it is the
-    # release validation run rather than day-to-day feedback.
-    branches: [main, dev]
+    # dev -> qa -> main. `dev` is where work lands and is meant to be pushed
+    # to often: these are the FAST checks, so a mistake surfaces in minutes.
+    # `qa` is the release candidate — it runs these too, plus the expensive
+    # suite in qa.yml. `main` only ever moves at release time, to a tagged
+    # commit that was already green on qa.
+    branches: [main, dev, qa]
   pull_request:
 
 # WHY THE SIBLING CHECKOUTS — this is NOT a monorepo.
@@ -45,12 +47,12 @@ jobs:
       - uses: actions/checkout@v5
         with:
           repository: freemkv/libfreemkv
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: libfreemkv
       - uses: actions/checkout@v5
         with:
           repository: freemkv/freemkv-unlock
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
       - name: Resolve siblings from their dev tips
         shell: bash
@@ -82,12 +84,12 @@ jobs:
       - uses: actions/checkout@v5
         with:
           repository: freemkv/libfreemkv
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: libfreemkv
       - uses: actions/checkout@v5
         with:
           repository: freemkv/freemkv-unlock
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
       - name: Resolve siblings from their dev tips
         shell: bash
@@ -117,12 +119,12 @@ jobs:
       - uses: actions/checkout@v5
         with:
           repository: freemkv/libfreemkv
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: libfreemkv
       - uses: actions/checkout@v5
         with:
           repository: freemkv/freemkv-unlock
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
       - name: Resolve siblings from their dev tips
         shell: bash
@@ -149,12 +151,12 @@ jobs:
       - uses: actions/checkout@v5
         with:
           repository: freemkv/libfreemkv
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: libfreemkv
       - uses: actions/checkout@v5
         with:
           repository: freemkv/freemkv-unlock
-          ref: dev
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
       - name: Resolve siblings from their dev tips
         shell: bash