docs(arch): Add ARCHITECTURE.md and CLAUDE.md, init repo

Bring the Blanton Tera Term TTL test suite under version control and
document how the pieces fit together.

- ARCHITECTURE.md: A/B/C script roles, host-to-DUT-to-FPGA data path,
  config/settings/profile data models, PCIe AER + EDAC topology table,
  10 key constraints, and 6 development phases derived from the
  Status_20260814 spreadsheet's On-Going items
- CLAUDE.md: stack, smoke-test commands, conventions, and the hardware
  footguns (per-unit BDF, VSPI vs VI2C timing, repeated START,
  STORE_USER_ALL, ARB_LOST false positives)
- secret/: gitignored credential store with README + .example template,
  so the DUT login stops living in 1_Blanton_Script_A.ttl
- .gitignore: secret/*, For_AI/, *.log, publish/, *.DSN

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014RetWKFZFG1ZHcitQAyhwM

src/Script_ABC_Blanton/config.ttl

@@ -0,0 +1,15 @@
+;================================================================
+; User Configuration
+;================================================================
+strTestcase="Margin"
+project_name = "Blanton"
+
+EN_Margin         = 1  ; 1: Enable Margin Test, 0: Disable Margin Test
+
+EN_log            = 1  ; 1: Enable log, 0: Disable log
+;================================================================
+; Prompt Definitions
+;================================================================
+prompt_login = "sonic login:"
+prompt_sonic = "admin@sonic:~$"
+prompt_sonic_root = "root@sonic:~#"