feat: add Banking TUI shell using bubbletea

Add an 80s-style green-on-black bank terminal shell ("banking") using
charmbracelet/bubbletea for full-screen TUI rendering over SSH.

Screens: login, main menu, account summary, account detail with
transactions, wire transfer wizard (6-step form capturing routing
number, destination, beneficiary, amount, memo, auth code), transaction
history with pagination, secure messages with breadcrumb content (fake
internal IPs, vault codes), change PIN, and hidden admin access (99)
that locks after 3 failed attempts with COBOL-style error output.

All key actions (login, navigation, wire transfers, admin attempts) are
logged to the session store. Wire transfer data is the honeypot gold.

Configurable via [shell.banking] in TOML: bank_name, terminal_id, region.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

oubliette.toml.example

@@ -24,6 +24,11 @@ password = "admin"
 # password = "fridge"
 # shell = "fridge"
 
+# [[auth.static_credentials]]
+# username = "teller"
+# password = "banking"
+# shell = "banking"
+
 [storage]
 db_path = "oubliette.db"
 retention_days = 90
@@ -38,6 +43,12 @@ hostname = "ubuntu-server"
 # banner = "Welcome to Ubuntu 22.04.3 LTS (GNU/Linux 5.15.0-89-generic x86_64)\r\n\r\n"
 # fake_user = ""  # override username in prompt; empty = use authenticated user
 
+# Per-shell configuration (optional).
+# [shell.banking]
+# bank_name = "SECUREBANK"
+# terminal_id = "SB-0001"   # random if not set
+# region = "NORTHEAST"
+
 # [detection]
 # enabled = true
 # threshold = 0.6          # 0.0–1.0, sessions above this trigger notifications