Add function inventory (.pdata), signature generation, and export/PDB symbols

Three reversing capabilities on the win32 surface plus a pure sig-gen handler:

- vmie_win32_functions enumerates a module's functions from the exception
  directory (.pdata RUNTIME_FUNCTION), folding unwind chain continuations into
  their primary - authoritative non-leaf boundaries, not prologue heuristics.
- vmie_win32_exports resolves the export table to {name, rva, ordinal,
  forwarded}: named functions with no PDB or network. vmie_win32_pdb_ref pulls
  the CodeView/RSDS {guid, age, pdb} from the debug directory - the symbol-server
  key for any module (full PDB parsing stays out of scope).
- sig_generate (siggen.h) builds a unique masked signature for a code span,
  wildcarding the rel/RIP-relative displacement bytes the x86 decoder locates and
  growing until it matches the scope exactly once - the dual of sigscan.

The decoder now also reports disp_off/disp_len so a caller can mask the floating
bytes. The MZ/PE walk gains one shared data-directory accessor and one shared
CodeView/RSDS parser; the kernel bootstrap is moved onto both, removing its
private copies - one PE parser in the tree.

src/engine/include/pe.h

@@ -60,4 +60,36 @@ bool pe_section(mem_view_t v, uint64_t module_base, const char* name,
 int vmie_pe_section(vmie_mem* m, uintptr_t cr3, uint64_t module_base,
                     const char* name, uint8_t* buf, size_t bufcap, mem_view_t* out);
 
+/* OptionalHeader DataDirectory indices used across the engine. */
+#define PE_DIR_EXPORT     0u    /* IMAGE_DIRECTORY_ENTRY_EXPORT    */
+#define PE_DIR_DEBUG      6u    /* IMAGE_DIRECTORY_ENTRY_DEBUG     */
+#define PE_DIR_EXCEPTION  3u    /* IMAGE_DIRECTORY_ENTRY_EXCEPTION (.pdata) */
+
+/* Read one OptionalHeader DataDirectory entry of the PE32+ image based at `base`
+ * in the address space `cr3`. This is the SINGLE data-directory accessor used by
+ * every directory walk in the engine (.pdata / export / debug) - it walks the
+ * DOS+NT headers from `base` once and reads DataDirectory[idx].
+ *   idx  - directory index (PE_DIR_*).
+ *   rva  - receives DataDirectory[idx].VirtualAddress (0 if the directory is
+ *          absent); never NULL.
+ *   size - receives DataDirectory[idx].Size; may be NULL.
+ * Returns 0 on success (rva/size filled), -1 if the headers are unreadable. A
+ * present-but-absent directory reports rva==0 with return 0. */
+int pe_data_dir(vmie_mem* m, uintptr_t cr3, uint64_t base, unsigned idx,
+                uint32_t* rva, uint32_t* size);
+
+/* Extract a module's CodeView RSDS reference from its debug directory. This is
+ * the SINGLE debug-dir/RSDS parser in the engine, shared by the kernel bootstrap
+ * (host.c) and the public vmie_win32_pdb_ref - there is no second copy.
+ *   base       - image base VA in `cr3`.
+ *   guid[16]   - receives the PDB GUID (in-memory byte order); never NULL.
+ *   age        - receives the PDB age; never NULL.
+ *   name       - receives the NUL-terminated PDB file name; never NULL.
+ *   namecap    - capacity of `name` (>= 1). The name is truncated to namecap-1.
+ * Walks PE_DIR_DEBUG for an IMAGE_DEBUG_TYPE_CODEVIEW entry whose payload starts
+ * with 'RSDS', then reads {guid, age, name}. Returns 0 on success, -1 if there
+ * is no debug directory, no CodeView/RSDS entry, or the bytes are unreadable. */
+int pe_pdb_ref(vmie_mem* m, uintptr_t cr3, uint64_t base,
+               uint8_t guid[16], uint32_t* age, char* name, size_t namecap);
+
 #endif /* VMIE_PE_H */