[codegen] annotate member-access expressions with concrete class types

[cs01]

Before

`obj.field` expressions where the object is a concrete class weren't cached in the typeOf map. Codegen live-resolved them every time.

After

Member-access expressions whose resolved type has `sourceKind === "class"` are annotated in the typeOf cache.

Description

Narrower relanding of the reverted #662. That PR also included `sourceKind === "interface"`, which caused x86-64-only Stage 0→Stage 1 self-hosting segfaults (passed on arm64, failed on x86-64 Linux CI and macOS CI). Root cause TBD — the class-dispatch path produces arch-divergent IR under `-O2` when an interface answer comes from the annotator cache instead of live-resolution.

Reproduced locally via `scripts/linux-x64.sh verify` (added in #667). Class-only filter passes full 3-stage bootstrap on both arm64 macOS and x86-64 Linux (via podman).

Verification

• arm64 macOS: `npm run verify` PASSED
• x86-64 Linux (podman): `bash scripts/linux-x64.sh verify` PASSED (all 3 bootstrap stages)

Refs #658. Interface-kind member_access annotation remains deferred pending x86-64 UB root-cause.

[github-actions]

Benchmark Results (Linux x86-64)

Benchmark	C	ChadScript	Go	Node	Place
Fibonacci	0.816s	0.763s	1.559s	3.158s	🥇
Hash Map Lookup	0.128s	0.065s	0.093s	0.130s	🥇
Regex Match	0.016s	0.005s	0.021s	0.005s	🥇
Binary Trees	1.606s	1.319s	2.775s	1.239s	🥈
Cold Start	0.8ms	0.9ms	1.3ms	28.6ms	🥈
File I/O	0.123s	0.096s	0.089s	0.208s	🥈
JSON Parse/Stringify	0.036s	0.053s	0.178s	0.138s	🥈
N-Body Simulation	1.672s	2.123s	2.206s	2.387s	🥈
SQLite	0.052s	0.372s	0.506s	0.440s	🥈
Monte Carlo Pi	0.389s	0.410s	0.406s	2.269s	🥉
Quicksort	0.215s	0.259s	0.213s	0.262s	🥉
Sieve of Eratosthenes	0.016s	0.026s	0.020s	0.040s	🥉
String Manipulation	0.008s	0.018s	0.017s	0.037s	🥉
Matrix Multiply	0.476s	0.681s	0.570s	0.379s	#4

CLI Tool Benchmarks

Benchmark	ChadScript	grep	node	xxd	Place
Hex Dump	0.571s	—	1.003s	0.134s	🥈
Recursive Grep	0.021s	0.011s	0.106s	—	🥈