Add CLAUDE.md describing the tool, pipeline and dev commands

CLAUDE.md

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+# ArgTyper
+
+A single Go binary that adds missing PHP parameter types from the literal values
+passed into local calls. No PHP, Composer or PHPStan needed at runtime. Built on
+[php-parser-in-go](https://github.com/rectorphp/php-parser-in-go).
+
+## What it does
+
+Reads every call site, sees the type of each literal argument (`f(324)` -> `int`),
+and writes that type back onto the untyped parameter. It works on the syntax tree
+only - no full type inference - so it stays fast and covers the safe cases:
+literals into statically resolvable targets (`new X()`, `X::method()`,
+`self::method()`, `$this->method()`, plain functions). Everything else is skipped.
+
+## How it works
+
+The run in `main.go` is a three-stage pipeline over the project's PHP files:
+
+1. **Collect** - record the type of each literal argument at every call site.
+2. **Resolve** (aggregate) - group records per parameter position, keep only the
+   unambiguous ones: a single type, or a single type plus `null` (nullable).
+3. **Apply** - add each resolved type to declarations still missing one and
+   reprint the file, leaving untouched code byte-for-byte.
+
+Skip rules: parameters that already have a type; parameters with conflicting
+types (ambiguous); magic methods except `__construct`; methods that may override
+a parent or interface (including vendor), unless private or a constructor.
+
+## Packages (`internal/`)
+
+- `finder` - locate project and vendor PHP files, and the scanned code dirs
+  (`src`, `lib`, `app`, `test`, `tests`).
+- `phpast` - parse PHP source and traverse the AST.
+- `symbols` - collect project enums and constants so argument values referencing
+  them resolve to a type.
+- `valuetype` - map a literal expression to its type.
+- `collect` - walk call sites and produce the argument-type records.
+- `inherit` - inheritance table used to skip overriding methods.
+- `aggregate` - resolve records into one type per parameter, dropping ambiguous.
+- `apply` - add resolved types to parameter declarations and reprint.
+- `diff` - unified diff, used by `--dry`.
+
+## Commands
+
+```bash
+argtyper add-types [project-path] [--dry]
+```
+
+`project-path` defaults to `.`. `--dry` prints the diff without writing.
+
+Dev tasks via `Makefile`:
+
+- `make build` - compile the `argtyper` binary
+- `make test` - `go test -race ./...`
+- `make check` - vet + build + test
+
+## CI
+
+`.github/workflows/build.yaml` runs four required jobs, mirroring
+php-parser-in-go and pinned to Go `1.26.6`:
+
+- `build` - vet, build, test -race, `go mod tidy` check
+- `format` - `gofmt -s` and `go fix`
+- `analysis` - gopls modernize and golangci-lint
+- `security` - govulncheck