[Push] Persist target path mappings with pull state

[adamziel]

This stores the resolved pull path mapping with each target relationship, so later commands can address the same local tree without repeating preflight.

path-mapping.json records the target document root, canonical local tree, and resolved remote/local prefix rules. The first mapping is immutable: reusing the same target and state directory with another local tree fails with an instruction to use another --state-dir.

Relationship discovery reads the mapping file. The relationship directory remains keyed only by the target URL after URL user-info, SECRET_KEY, and the site-export-api endpoint alias are removed. Before file work begins, the old root-level pull state moves into the relationship directory after preflight identifies the target and local tree. When apply-runtime receives a flattened root which no longer matches the original local tree, it selects the sole persisted pull state or refuses an ambiguous state directory.

Stacked on #413.

[github-actions]

Pull pipeline performance — large-directory

Site: large-directory · 2,000+ plus targeted file-transfer scenarios files · 10,000 posts · 25,000 postmeta · PHP 8.5.9

Stage	PR	trunk	Δ	Status	Details
playground-sqlite-db-pull	9.32 s	9.29 s	⚪ +36 ms (+0.4%)	✓	condition=db-pull in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=lexer native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=selected trunk: condition=db-pull in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=lexer native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=selected
playground-sqlite-db-apply	3.65 s	3.64 s	⚪ +16 ms (+0.4%)	✓	condition=db-apply to SQLite in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=parser native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=verified native_ast=WP_MySQL_Native_Parser_Node sqlite_driver_parser=verified trunk: condition=db-apply to SQLite in PHP.wasm runtime=php.wasm 8.3 wp_mysql_parser=enabled mode=parser native_lexer=verified native_token_stream=WP_MySQL_Native_Token_Stream native_token_count=18 native_parser=verified native_ast=WP_MySQL_Native_Parser_Node sqlite_driver_parser=verified
Total	12.97 s	12.92 s	⚪ +52 ms (+0.4%)

_{Numbers carry runner noise; treat single-run deltas as directional, not authoritative.}

_{📈 Trunk performance history — commit-by-commit timeline.}