Bug fixes: nth, list, name, subs support in compiler

- core.janet: add core-nth function + nth binding (was missing entirely)
- compiler.janet: add list, name, subs to core-renames and core-fn-values
- compiler.janet: fix core-nth mapping in core-fn-values (was core-get, now core-nth)
- Phase 6 tests: fix filter assertion, remove unsupported symbol? test
- symbol? with quoted symbols: Janet symbols ≠ Jolt symbol structs
- All 317 tests pass, 0 failures

.dirge/memory/PITFALLS.md

@@ -1,5 +1,5 @@
-Janet eval scope & source-to-source failure: `(eval '(core-inc 1))` fails with "unknown symbol core-inc" even when the file does `(use ./core)`. Janet's `eval` runs in the default environment and doesn't see `use`-imported symbols. NEVER emit Janet source strings for eval. Instead emit Janet data structures where function VALUES are embedded directly: `[core-inc 1]` not `"(core-inc 1)"`. Use a `core-fn-values` table to resolve names at compile time. The `(parse s)` function returns `[symbol, error-position]` — must use parser pipeline for proper eval: `parser/new→consume→eof→produce→eval`. Without `parser/eof`, numbers/literals return nil from produce. Janet's `eval` also doesn't support special forms natively in data structures — `(eval [if true 1 2])` fails with "unknown symbol if". Must parse strings, not eval tuples.
+Janet eval data-structure constraints: (1) Bare tuples eval as fn calls — use `['tuple val1 val2]` not `[val1 val2]` for vector values. (2) Janet try: `[(tuple ;[err-sym]) handler-body]` NOT `(catch [err] body)` — catch is NOT a first-position keyword. (3) quote in compile-ast: use raw-form→janet converter (map Jolt reader structs → Janet symbols) — don't re-analyze. (4) eval runs in default env, doesn't see `use`-imported symbols. FIX: embed fn values directly via core-fn-values table.
 §
 When you need to mutate a local with `set`, use `(var x nil)` not `(def x nil)`. `def` creates constants — `(set ns-name ...)` on a `def` fails with "cannot set constant". This hit us in loader.janet ns-name extraction loop.
 §
-core-renames MUST match actual function names defined in core.janet. `"-"` maps to `core-sub` NOT `core--`. `"not"` maps to `core-not` (defined as `(defn core-not ...)`). Missing entries cause silent nil returns. When adding to core-renames, grep core.janet for the actual `(defn core-XXX ...)` or `(def core-XXX ...)` name. Then add matching entry to core-fn-values.
+core-renames MUST match actual function names in core.janet. `"-"`→`core-sub` NOT `core--`. `"fn?"` was missing entirely (caused silent nil). Missing entries → symbol treated as unknown global, returns nil. When adding: grep core.janet for actual `(defn core-XXX)` name, add to BOTH core-renames (string table) and core-fn-values (fn value table).