docs: add operating manual, fix cross-references after doc restructure

- Commit CLAUDE.md + AGENTS.md so a fresh clone has the operating manual and
  the ABI/no-game-logic rules (trimmed of stale phase status; the personal
  pd_port path removed; points at the split docs).
- Sweep every stale doc reference across the tree after the restructure:
  PCPortResearch.md -> internals.md / dev/findings.md,
  PORT-LEARNINGS.md -> porting-notes.md,
  AGENT-WORKFLOW.md -> dev-process.md,
  docs/{GRAPHICS-BACKLOG,HANDOFF-ARCHIVE,GE-ENV-PROBES,LEVEL-*,TEXTURE-GLITCH-ANALYSIS,AUDIT-M6-*,AUDIO-PLAN}.md -> docs/dev/.
- Drop the superseded docs/PLAN-linear-level-sweep.md.
- docs/HANDOFF.md + docs/BACKLOG.md stay local-only (rolling working files);
  CLAUDE.md now handles their absence in a fresh clone.

assets/animationtable_data.h

@@ -198,7 +198,7 @@
 // as the defines above, which is to index into ptr_animation_table.
 
 #if defined(__x86_64__)
-/* D34 (docs/PCPortResearch.md): on N64 this segment links at VMA 0
+/* D34 (docs/dev/findings.md): on N64 this segment links at VMA 0
  * (ge007.ld), so &ANIM_DATA_x is the record's offset within the
  * animation_data segment and game code re-bases it with
  * `(s32)&ANIM_DATA_x + ptr_animation_table`. A PE image cannot be placed

assets/obseg/setup/e/UsetuplenZ.c

@@ -770,7 +770,7 @@ s32 intro[] = {
     _mkword(0, _mkshort(0, 1)), 0, -1, 0,
     /* Type = Credits; index = 3 */
 #if defined(PORT)
-    /* PC port (docs/PCPortResearch.md §11): pointer-in-word static initializer
+    /* PC port (docs/dev/findings.md §11): pointer-in-word static initializer
      * is a hard error on the 64-bit host GCC; the real value comes from ROM
      * data loading in Phase 2. */
     _mkword(0, _mkshort(0, 8)), 0,

assets/obseg/setup/j/UsetuplenZ.c

@@ -773,7 +773,7 @@ s32 intro[] = {
     _mkword(0, _mkshort(0, 1)), 0, -1, 0,
     /* Type = Credits; index = 3 */
 #if defined(PORT)
-    /* PC port (docs/PCPortResearch.md §11): pointer-in-word static initializer
+    /* PC port (docs/dev/findings.md §11): pointer-in-word static initializer
      * is a hard error on the 64-bit host GCC; the real value comes from ROM
      * data loading in Phase 2. */
     _mkword(0, _mkshort(0, 8)), 0,

assets/obseg/setup/u/UsetuplenZ.c

@@ -717,7 +717,7 @@ s32 intro[] = {
     _mkword(0, _mkshort(0, 1)), 0, -1, 0,
     /* Type = Credits; index = 3 */
 #if defined(PORT)
-    /* PC port (docs/PCPortResearch.md §11): pointer-in-word static initializer
+    /* PC port (docs/dev/findings.md §11): pointer-in-word static initializer
      * is a hard error on the 64-bit host GCC; the real value comes from ROM
      * data loading in Phase 2. */
     _mkword(0, _mkshort(0, 8)), 0,