feat: preset abstraction + --preset flag + split: config section (#14)

[NickMoignard]

What & why

First slice of preset-based semantic explosion (#14). Establishes the preset abstraction and the config/CLI plumbing that later slices (#15 rule engine, #16 SQL sidecar) hang rules on. No semantic extraction rules yet — this is the additive foundation, and existing behavior is unchanged.

Changes

• internal/preset (supersedes internal/profile): a Preset now bundles split option defaults (MaxLines, MaxDepth) with IDKeys. QuickSight()/Generic()/ByName() carried over; profile package deleted.
• --preset flag (default quicksight) on split; --profile kept as a hidden deprecated alias so existing scripts keep working.
• Config split: section (preset, max_lines, max_depth, id_keys) + matching YAMLX_SPLIT_* env vars. Optional fields use nil pointers / empty slices so "unset" lets the preset default stand rather than clobbering it with a zero.
• Precedence resolved in resolveSplitOptions: flags > env > config file > preset > engine defaults. Loaded config is stashed on the command context for the split command to read.

Verification

• go build ./..., go test ./..., golangci-lint run all green.
• New tests: preset defaults; config split: file/env/precedence + invalid-int error; identity.txtar updated to --preset (+ --profile alias + unknown-preset usage error); new preset-config.txtar proving the config block drives the split, a flag overrides it, and it still round-trips.
• Smoke-tested on a real fixture: --preset quicksight reproduces prior output, --profile alias works and is hidden from help, unknown preset exits 2, YAMLX_SPLIT_MAX_LINES env override applies, verify ok.

Notes

• --profile is now hidden/deprecated in favor of --preset — flagging in case you'd rather keep --profile visible.
• config.Config is no longer ==-comparable (nested split: struct); the one test relying on that now uses reflect.DeepEqual.

Closes #14.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR introduces a new preset abstraction (superseding profile) and wires it through the CLI and config system so split defaults can be driven by --preset, config split: settings, and YAMLX_SPLIT_* env vars—while preserving existing behavior via a hidden --profile alias.

Changes:

• Added internal/preset with Preset (defaults + identity keys) and QuickSight/Generic/ByName helpers; removed internal/profile.
• Added config support for a split: section (preset, max_lines, max_depth, id_keys) and matching *_SPLIT_* env var overrides.
• Updated split CLI plumbing to resolve options with precedence flags > env > config file > preset > engine defaults, plus updated script-based fixtures/tests.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/profile/profile.go	Removed old profile abstraction (identity-key-only).
internal/preset/preset.go	Introduces preset abstraction carrying split defaults + ID keys.
internal/preset/preset_test.go	Updates tests to preset package and adds default-threshold coverage.
internal/config/config.go	Adds SplitConfig and env parsing for SPLIT_* keys.
internal/config/config_test.go	Adds tests for split config parsing, env overrides, and invalid ints.
internal/cli/testdata/script/preset-config.txtar	New script proving config-driven split behavior + precedence.
internal/cli/testdata/script/identity.txtar	Updates scripts to --preset, retains --profile alias coverage.
internal/cli/logger.go	Adds a new context key for stashing resolved config.
internal/cli/commands.go	Implements resolveSplitOptions, adds --preset + hidden --profile alias.
internal/cli/cli.go	Stashes loaded config on command context for split option resolution.

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