docs: delete BUGS.md; fix spec drift for this session's features

- Remove BUGS.md (no open compiler bugs) and the dead README reference to it.
- Update RSScript_v0.7_Spec.md to document features shipped after the v0.7
  refresh, which had drifted out of the spec:
  - §6.11 type aliases (generic + non-generic, transparent, expanded everywhere).
  - §14.1 struct field defaults (construction helpers).
  - §10.9 named function values (forwarding-closure desugar).
  - §14.8 qualified module value/type access (module.CONST / module.Variant in
    value and pattern position, module.Type in type position), `use module.*`
    glob import, `read`-of-qualified-call precedence, and the reserved
    `__rss_`/`__rsscript_` generated-symbol namespace.
  - Refreshed the Implemented-surface index to match.

Spec-reading package tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: olwang

BUGS.md

@@ -473,7 +473,7 @@ rss test     [--all] [--json] [--filter <substring>]
 - `rss pkg publish --dry-run` runs pre-publish checks without uploading and reports whether the package is ready.
 - `rss run` lowers a single file (or a package with `src/main.rss`) to a temporary Rust package and delegates to `cargo run`; package lowering carries enabled `[native.rust]` wrappers through as generated Cargo path dependencies and maps `native/bindings.rssbind.toml` call bindings into generated Rust calls. `--dry-run` prints the generated `Cargo.toml`, lowered Rust, and cargo invocation without executing it; `--release` delegates to Cargo's release profile, `--out-dir` keeps the generated package, and arguments after `--` reach the program through the core `Args` API.
 
-> **Performance — use a release-built `rss` for package-scale checking.** On large, generics-heavy packages, `rss check` / `rss pkg` can be noticeably slow when run from a **debug** build of the compiler, because generic type-argument substitution currently re-parses type strings at each nesting level (a known, deferred ~O(n³) path — see `BUGS.md` RSS-11). The debug build leaves that path unoptimized; a release build optimizes it enough to be comfortable. For repeated package-wide validation (e.g. an inner edit→check loop on a big codebase), build the compiler once in release and use that binary:
+> **Performance — use a release-built `rss` for package-scale checking.** On large, generics-heavy packages, `rss check` / `rss pkg` can be noticeably slow when run from a **debug** build of the compiler, because generic type-argument substitution currently re-parses type strings at each nesting level (a known, deferred ~O(n³) path in generic substitution). The debug build leaves that path unoptimized; a release build optimizes it enough to be comfortable. For repeated package-wide validation (e.g. an inner edit→check loop on a big codebase), build the compiler once in release and use that binary:
 >
 > ```sh
 > cargo build --release --bin rss