feat: make 1P field name configurable via OP_FIELD

[busla]

Why

Two fragility issues with the 1Password field lookup:

1. Hardcoded field name: the fallback was the literal string "API Key" in both wrappers. op read is exact-match and case-sensitive — users with API key (lowercase k) or any non-standard naming hit a silent retrieval failure. The diagnostic block from PR fix(claude-env.sh): capture op stderr to surface actual 1P errors #12 confirmed this as the most common real-world cause.
2. No discoverability: even with the field name configurable, users have to know what fields exist in their 1P item. The installer prompted for a free-form string with no guidance.

What

Part 1 — OP_FIELD configurability (commit 1)

Adds OP_FIELD as a configurable variable, defaulting to "API Key" so existing installs work unchanged. Five touchpoints:

File	Change
claude-env.sh	New OP_FIELD="API Key" default + ${OP_FIELD} in lookup + reference in diagnostic block
claudestart.ps1	New $OP_Field = "API Key" default + extend local.env regex to include OP_FIELD and OP_ACCOUNT (same fragility class) + $OP_Field in lookup + reference in diagnostic block
install.sh	Prompt for the field, read existing value as default, serialize to local.env
install.ps1	Matching PowerShell prompt + serialization

Part 2 — Field enumeration in installer (commit 2)

After OP_ITEM is entered, the installer calls op item get <item> --vault <vault> to enumerate the actual fields and shows them as a numbered list. User can either type the field name or pick by number. Falls back to free-form prompt with a warning if op enumeration fails (op missing, not signed in, item doesn't exist).

  Fields available in op://Employee/ai.apro.is litellm:
      [1] password
      [2] username
      [3] notesPlain
      [4] API Key
      [5] genai-azure
      [6] management

  1Password field name (or number) [API Key]: 4

Implementation notes:

• op item get does NOT accept the op://Vault/Item syntax (only op read does). Installer parses OP_ITEM into --vault + item name.
• Bash JSON parsing without jq: scope to the "fields" array via awk (URL entries also have "label" keys), then grep field labels. Pretty-printed JSON has whitespace after colons; the regex tolerates it.
• PowerShell side uses ConvertFrom-Json and walks $parsed.fields[].label directly.

Backwards compatibility

Existing local.env files without OP_FIELD keep working — each wrapper sets the default before sourcing/parsing local.env. Users get the override capability when they re-run the installer, which preserves their current values as prompt defaults.

Verification

• ✅ OP_FIELD="custom-name" in local.env propagates to runtime variable (functional test against claude-env.sh)
• ✅ All lookup sites use the variable; only default declarations and explanatory comments still mention "API Key"
• ✅ Field enumeration against a real 1P item returns the correct labels (password, username, API Key, etc. — no website from the URL section)
• ✅ Bash syntax check passes for both claude-env.sh and install.sh

🤖 Generated with Claude Code