docs(keycloak-session-store): import the session-storage lab as a new project

The keycloak project ended with four open questions that design could not
settle. A two-VM lab was built to answer them by measurement, and this is
that material: 26 experiments, 125 raw command outputs, 22 browser captures.

Follows the import procedure in README.md.

  source/     the originating repository verbatim — 78 documents, 28 SVGs,
              8 manifests, plus .source-revision recording the commit
  final/      the SSOT
    document.md   729 lines written from the 29 experiment documents, not
                  concatenated: what was predicted, what was measured, and
                  where the measurement itself was wrong
    evidence/raw    125 outputs, flattened to <experiment>__<file> because
                    the originals collided (01-baseline.txt appeared three
                    times) and the audit only globs the top level
    evidence/meta   one per raw file; command and exitCode are null and the
                    README says why rather than inventing them
    evidence/browser  22 captures
    assets/       three diagrams through techviz
    .techviz/     their VizSpecs

A separate project rather than an addition to keycloak: the B-layer answers
that project's four questions, but the A, C and D layers are about cluster
failure, SSO and operations, and one document.md should hold one subject.
The four question records there can point here through 관계.

Recorded rather than papered over: only three of the 28 diagrams were
remade. The repository forbids hand-drawn SVG and forbids titles inside the
canvas; all 28 originals carry both, so converting them is redrawing, not
reformatting. They stay in source/ and the gap is written into the document.

verify-pipeline.py passes. audit-records.py reports no issues.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/clean-architecture-backend-template/final/evidence/raw/tl-rotation-defect-reproduced.txt

@@ -0,0 +1,19 @@
+--- messaging: the defect was closed and pinned by a contract test
+22: * <p>{@code resolve} was get → fetch → put → clear with no synchronization. Two callers rotating
+23- * the same credential both read the same old runtime and both fetched a replacement: one
+24- * replacement was dropped from the map without ever being cleared — a secret left in memory that
+25- * nothing owns — and the loser could clear material the winner was still using.
+26- */
+
+--- grpc: AtomicReference used as a plain holder
+70:    return state.get().current();
+75:    return Optional.ofNullable(state.get().draining());
+89:    State observed = state.get();
+103:    state.set(new State(next, observed.current(), deadline));
+113:    State observed = state.get();
+119:    State observed = state.get();
+120:    state.set(new State(observed.current(), null, null));
+--- compareAndSet / updateAndGet / synchronized in that file:
+0
+--- and the javadoc already names the race:
+83:   *     usual reason for one is two rotators racing