fpga: rename "quirk" to "caveat"

"quirk" was unclear jargon; "caveat" matches the wording already used in
the README/CLAUDE.md ("Xilinx caveats"). Renames the struct field, the
FPGA_QUIRK_* macro, the fpga_info output and the docs. No behaviour
change.

modules/fpga/fpga.h

@@ -9,7 +9,7 @@
  *   - private IR opcodes (USER1, CFG_IN, JPROGRAM, …) needed for
  *     configuration and for the BSCAN proxy bridge (Phase 2.5)
  *   - path to the BSCAN proxy bitstream
- *   - per-target quirks
+ *   - per-target caveats (known hardware gotchas)
  *
  * Adding an FPGA = one entry in fpga_registry[] + its .bsd in
  * bsdl_files/ + (optionally) its proxy .bit in bscan_proxies/.
@@ -24,8 +24,8 @@ typedef enum {
     FPGA_FAMILY_XILINX_USP,
 } fpga_family;
 
-/* Quirk flags */
-#define FPGA_QUIRK_CCLK_VIA_STARTUP   (1u << 0)  /* CCLK not directly drivable in EXTEST */
+/* Caveat flags: known hardware gotchas for a part. */
+#define FPGA_CAVEAT_CCLK_VIA_STARTUP   (1u << 0)  /* CCLK not directly drivable in EXTEST */
 
 typedef struct {
     const char    *name;             /* human-readable part name */
@@ -45,7 +45,7 @@ typedef struct {
     unsigned int   ir_isc_disable;
 
     const char    *proxy_bitstream;  /* path under bscan_proxies/, NULL if not yet available */
-    unsigned int   quirks;
+    unsigned int   caveats;          /* FPGA_CAVEAT_* flags */
 } fpga_target;
 
 /* Registry access */