fix(storage create-table --if-not-exists): report actual existing schema on skip (#349)

[padak]

Summary

Closes #349 (the deferred follow-up filed before #348 merged).

storage create-table --if-not-exists returned action: "skipped" with a
columns / primary_key / name envelope that re-echoed the caller's
request instead of reporting the existing table's real schema. A caller
probing the skipped envelope to discover the actual shape of a pre-existing
table got the wrong values whenever the existing table differed from what was
requested.

The get_table_detail(target_id) lookup that already runs to confirm the table
exists is now also the source of the returned schema:

• columns / primary_key / name → the existing table's actual values
• requested_columns / requested_primary_key → the caller's request, preserved
• schema_drift: bool → true when the existing table diverges from the request
  (set comparison, so column/PK reordering is not a false positive)

Human-mode output prints the actual schema on a skip and emits a Warning: line
when schema_drift is true. The action: "created" envelope is unchanged.

Scope

• No new flag, no signature change — refines the existing --if-not-exists
  envelope only.
• HTTP router needs no change: create_table returns the service dict verbatim,
  so the new fields flow through kbagent serve automatically.
• Bumps 0.47.0 → 0.47.1 (behavior change to a shipped envelope).

Envelope (skipped)

{
  "table_id": "in.c-foo.bar",
  "name": "bar",
  "columns": ["id", "name"],
  "primary_key": ["id"],
  "requested_columns": ["id", "name", "extra"],
  "requested_primary_key": ["extra"],
  "schema_drift": true,
  "action": "skipped",
  "skip_reason": "table already exists"
}

Tests

• tests/test_storage_write.py — skipped returns actual schema (not request);
  schema_drift true on divergence, false on match; order-insensitive drift;
  human-mode warning + actual-schema render.
• tests/test_e2e.py::TestE2E_0_47_0_NewSurfaces — extended the existing
  round-trip to assert the skipped envelope reports actual columns + the
  requested_* mirror, plus a divergent-request call asserting schema_drift: true.

Plugin sync-map

Behavior change (not a new command), so the touched surfaces are:

• src/keboola_agent_cli/changelog.py — 0.47.1 entry
• src/keboola_agent_cli/commands/context.py — AGENT_CONTEXT note
• plugins/kbagent/skills/kbagent/references/gotchas.md — caveat replaced with
  the fixed-behavior note (since v0.47.1)
• plugins/kbagent/skills/kbagent/references/commands-reference.md
• plugin.json / marketplace.json / uv.lock via make version-sync

keboola-expert.md §3 not touched: the fix makes the envelope more trustworthy
(actual schema), introducing no new wrong-by-default behavior — the detailed note
lives in gotchas.md.

Checks

• make check green (lint + format + skill + version + changelog + error-codes + 3617 tests)
• make typecheck clean (the single unresolved-import warning on scripts/hatch_build.py is pre-existing, non-blocking)

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.