Epic: canclang rebuild — native C++ L1→L4 analyzer

[rahlk]

Rebuild canclang from scratch as a native C++/libTooling analyzer emitting canonical
schema v2, per the approved design spec (2026-07-08, kept locally). Locked decisions:
native C++20/CMake stack; clang::CFG for L3; SVF (flag-gated) for L2 + the L4 oracle;
orphan restart of main.

PR ladder (one child issue per rung; each rung's detailed plan is written when it starts):

• bootstrap: orphan restart, CMake skeleton, CLI contract, CI #4 bootstrap: orphan restart, CMake skeleton, CLI contract, CI
• L1: symbol table (-a 1) #5 L1: symbol table (-a 1)
• L1: resolver call-graph backfill (-a 2) #6 L1: resolver call-graph backfill (-a 2)
• caching + -j determinism (L1 scope) #7 caching + -j determinism (L1 scope)
• Neo4j projection + schema conformance #8 Neo4j projection + schema conformance
• packaging + release automation (v1 tag) #9 packaging + release automation (v1 tag)
• L3: CFG -> dominance/CDG -> DDG -> PDG (-a 3) #10 L3: CFG → dominance/CDG → DDG → PDG (-a 3)
• L2: SVF integration (--svf) #11 L2: SVF — bitcode pipeline, Andersen, call-graph merge (--svf)
• L4: oracle seam, summaries, SDG (-a 4) #12 L4: oracle seam, summaries, SDG (-a 4)
• CPG overlay in Neo4j #13 CPG overlay in Neo4j