Mask secret-looking app environment variable values

[nabramovitz]

What

Masks secret-looking values on the app Variables tab so they are only displayed on explicit request:

• Variables list: sensitive values render as •••••••• with a per-row Show/Hide toggle in the Value cell.
• All Variables block: values are deep-masked (including leaves inside VCAP_SERVICES and friends), with a single Show secrets / Hide secrets toggle in the card header.
• The edit dialog is intentionally left unmasked — opening Edit on a named variable is the explicit request, and masking there would break editing.

A value is considered sensitive when:

• its name matches pass|secret|token|private|key|cred (full mask), or
• it embeds credentials as scheme://user:pass@host (only the password is redacted, so host/port/path stay readable), or
• it contains a PEM private-key block (-----BEGIN … PRIVATE KEY-----, any variant) — masked under any variable name. Certificate blocks are public material and stay visible.

These are the same heuristics the Service Keys page already uses; they now live in one shared module (toCredentialField / maskEnvValue), so both surfaces stay in lockstep. As a side effect this change also removes an existing leak: the old Value cell exposed the full raw value in its hover title tooltip.

Also in this PR

• Deleted the env-var-view dialog component — orphaned by the earlier variable-editor rework, zero references (grep-verified with a positive control).
• Accessible names for the new toggles (Show value for <name>, Show secrets in All Variables).

Testing

• Unit: new specs for the classifier, the deep masker (nested objects/arrays, precedence, PEM variants, immutability), and the tab's masking projections. Full suite green.
• e2e: two new Playwright tests (per-row toggle and block toggle) asserting the mask literal is shown and the seeded secret value is absent from the DOM until revealed; both pass against a live CF.
• Live-verified twice in the running console against a real CF, including the add-variable flow: a secret-named variable and a PEM private key under an innocuous name (SERVER_CRT) both masked on first render.
• make check gate green end to end.

Deliberate ceilings, recorded in code comments: masking is leaf-based (a credentials container is recursed, not blanket-masked — matching Service Keys), and PEM detection keys on the armor header, so raw base64/DER key material under an innocuous name is not caught.

[norman-abramovitz]

LGTM