[Feature] Forge observation and doctor extensions (PR-3) #164

Problem

ainative doctor/status report installation state but have no concept of the
observed forge, remote candidates, Work Authority resolution state, or the
effective release source. Multi-Forge requires a read-only observation surface
that never dials out, never reads credentials, and never guesses a provider from
a hostname.

Source: Multi-Forge v1.3.2-final §55–59 (PR-3).

Expected outcome

ainative forge detect and ainative forge status describe what can be observed
locally about the project's remotes and features; doctor displays the effective
profile, feature set, Work Authority resolution state and release source — with
zero network, credentials, writes or persistent trust.

Acceptance criteria

• Blocked until PR-1 green.
• Commands ainative forge detect and ainative forge status exist and
  satisfy: network calls = 0, credentials = 0, writes = 0, persistent
  trust = 0.
• Provider hints: github.com → github, gitlab.com → gitlab,
  unknown/custom host → unknown; self-hosted provider detection is never
  guessed from hostname alone.
• Fork rendering: origin/upstream candidates are displayed without automatic
  preference; ambiguity is rendered (e.g. Resolution: AMBIGUOUS).
• Doctor extensions display: profile, assurance level, effective feature set,
  observed remote candidates, Work Authority resolution state, release source,
  release selection reason, release auth origin, unresolved ClaimAttempts —
  never credentials.
• Output is stable, machine-readable where the rest of the CLI is
  (--json), and derived through the shared feature projection.

Out of scope

• Provider network calls, credential lookup, trust persistence.
• Release source resolution implementation (PR-4A) — doctor only displays it once
  it exists; until then the current effective source is shown.
• Claims resolution logic (PR-2).

Context

• ainative/cli.py, ainative/lifecycle/status.py, machine_health.py.
• Depends on PR-1.

Dependencies

• Blocked by PR-1 ([Feature] Profiles / Features / State V2 (PR-1) #162).