fix(codex): skip per-task marketplace upgrades

[wjueyao]

What changed

• strip user-level [marketplaces.*] update sources from copied per-task Codex
  config
• preserve [plugins.*] entries so installed plugin capabilities continue
  loading from Multica's exposed shared plugins/cache
• remove incompatible skills.config entries using semantic TOML source
  ranges rather than line matching
• preserve unrelated model, profile, MCP, sandbox, and observability config
• cover dotted, inline, quoted, array-table, multiline-string, shared-config,
  and shared-plugin-cache behavior

Why

Each fresh isolated CODEX_HOME inherited the user's marketplace update
sources. Codex therefore repeated git remote probes and sometimes clones before
the first turn. Slow or unavailable network access could consume the 30-second
semantic inactivity window and fail the task before it emitted any progress
event.

The task still inherits enabled plugin entries and loads their installed code
from the shared cache; only marketplace lifecycle and network refresh are kept
in the shared user home.

Validation

• go test ./internal/daemon/execenv -count=1
• go test ./internal/daemon/... -count=1
• go vet ./internal/daemon/execenv
• git diff --check

Closes #5573

[vercel]

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