Build 21 docs + TCL fix: WNS +0.156ns, 139 DSP, tag v0.1.4-build21

Build 21 Vivado results extracted and documented:
- WNS +0.156 ns, WHS +0.064 ns, WPWS +0.361 ns (all timing met)
- 6,192 LUTs (4.6%), 9,064 FFs (3.4%), 16 BRAM (4.4%), 139 DSP48E1 (18.8%)
- Total power: 0.732 W
- Barrel-shift twiddle freed 1 DSP (140 -> 139) as expected
- TCL script fix: wrap check_timing in catch (Vivado 2025.2 bug)
- Updated release-notes.html, implementation-log.html, reports.html

9_Firmware/9_2_FPGA/scripts/build21_fft_e2e.tcl

@@ -309,7 +309,10 @@ if {[catch {report_exceptions -file "${report_dir}/13_exceptions.rpt"} err]} {
     puts "  WARNING: report_exceptions failed: $err"
     puts "  (Known Vivado 2025.2 issue — non-critical)"
 }
-check_timing -verbose -file "${report_dir}/13_check_timing.rpt"
+if {[catch {check_timing -verbose -file "${report_dir}/13_check_timing.rpt"} err]} {
+    puts "  WARNING: check_timing failed: $err"
+    puts "  (Known Vivado 2025.2 issue — non-critical)"
+}
 
 # Compile configuration summary into a single text file
 set summary_fh [open "${report_dir}/00_build21_summary.txt" w]