Lambe 0.4.0: drop XML, bare pipeline ops, MCP surface fixes

[hakimjonas]

Summary

• Drop XML support. The xmlToNative projection silently collapsed repeated sibling elements (last-wins map semantics) and dropped attributes entirely, producing wrong query results. Rather than ship a footgun, XML is removed pending a proper projection design (auto-arrayify siblings, preserve attributes). The rumil XML parser itself is unchanged and spec-compliant.
• Pipeline ops are now valid bare expressions with implicit . input. has("k"), length, keys, sum, filter(...), map(...) — standalone or inside map/filter. Equivalent to . | op. One-line parser change; 22 new tests.
• MCP surface improvements. Version now read from pubspec.yaml via build-time-generated lib/src/_version.dart (was hardcoded 0.1.0). CSV and TSV exposed in all three format enums (library already supported them). New output_format parameter on lambe_query for yaml/toml/csv/tsv/hcl output, matching the --to CLI flag. Tool descriptions rewritten to document real pitfalls (&&/||, bracket syntax for hyphenated keys, group_by shape).
• Doc-example test coverage. test/doc_examples_test.dart extracts every lam '...' from AI.md and every embedded query from the MCP server's Dart string literals (34 expressions), and asserts each parses. Prevents phantom-feature drift where LLM-drafted examples advertise syntax the parser doesn't implement.
• Phantom .. (recursive descent) removed from docs. It was advertised as a Markdown query operator but was never implemented.
• Fixed broken filter(has("resources") == false) example — which now works on its own merits thanks to the bare-op change.

Breaking

• Format.xml, OutputFormat.xml, and XML extension detection (.xml, .pom, .csproj, .svg) removed from the library.
• --format xml / --to xml CLI flags and the :to xml REPL command no longer accepted.

Non-breaking additions

• lambeVersion exported from package:lambe/lambe.dart.
• output_format parameter on the lambe_query MCP tool.
• csv, tsv in all three MCP format enums.
• tool/gen_version.dart + release workflow step.
• Bare pipeline ops as expressions — every existing query still works; the change is purely additive.

Test plan

• dart analyze lib bin test tool — no issues
• dart test — 547 pass (was 491 on main; added 22 bare-op tests + 34 doc-example tests)
• MCP server compiles and reports correct version via stdio initialize
• 13 ambiguity probes for the bare-op change ({length}, .length, keys[0], "(length)", length + 1, etc.) all resolve per prior semantics
• Release workflow end-to-end (will run when tag is pushed after merge)
• MCP registry publish step no longer fails on duplicate version (will run on tag)

Out of scope

• Re-introducing XML with a proper projection (future release, needs design discussion for attribute representation and sibling-list semantics).
• A generic Format.delimited to unify CSV/TSV under the delimited parser (deferred — the current csv/tsv split preserves a useful dialect-detection escape hatch).