feat: implement routine_management RPC methods (#84)

[aesslinger]

Summary

• Ports the builtin driver's PostgreSQL-dialect routine SQL builders (src-tauri/src/drivers/postgres/routines.rs) into a new src/handlers/routines.rs, and wires build_routine_call_sql, routine_create_template, drop_routine into the RPC dispatch table.
• Previously all three hit the not_implemented catch-all, so the host silently fell back to generic, non-PostgreSQL SQL — invalid call syntax for functions with OUT params, a template with no LANGUAGE plpgsql/$$ dollar quoting, and a bare DROP FUNCTION name with no signature that can't disambiguate overloads.
• routine_call_sql: SELECT * FROM fn(...) for functions (excludes pure OUT args, which PostgreSQL rejects in a function's call signature), CALL proc(...) for procedures (OUT args rendered as NULL placeholders, INOUT values echoed back by the server).
• routine_create_template: valid, re-runnable CREATE OR REPLACE FUNCTION/PROCEDURE ... LANGUAGE plpgsql AS $$ ... $$ scripts.
• drop_routine: resolves the routine's exact identity signature via pg_get_function_identity_arguments first, so an overloaded routine errors with a clear message instead of an ambiguous or wrong drop.

get_routine_edit_script is intentionally left alone — both the builtin and the host's plugin-bridge fallback already resolve it to get_routine_definition, which this plugin implements (per the issue's own note that this one isn't a gap).

Fixes #84.

Test plan

• cargo test --lib — 309 passed (11 new unit tests in routines_tests.rs, matching the builtin's own routine_management test module's expected outputs byte-for-byte)
• cargo clippy --all-targets -- -D warnings — clean
• cargo fmt --all -- --check — clean
• Confirmed the pre-fix binary returns Method not found (-32601) for all three methods against a live PostgreSQL instance, then confirmed the fix's binary returns correct results for the same requests
• Live end-to-end verification — not just string-shape checks, actually executed the generated SQL:
  • build_routine_call_sql for a function with OUT params generates SELECT * FROM "public"."fn_split"(5);, which executes and returns the correct OUT values
  • build_routine_call_sql for a procedure with an OUT param generates CALL "public"."sp_greet"('world', NULL);, which executes and returns the correct result
  • routine_create_template for both FUNCTION and PROCEDURE produces scripts that execute successfully and create a routine that then runs correctly when called
  • drop_routine on an overloaded function returns a clear "has N overloads" error and drops neither overload; on a non-overloaded function it drops cleanly; on a missing routine it returns a clear "not found" error

[github-actions]

Version suggestion

Based on this PR's title (feat) and the prerelease:rc label:

Current	1.0.0-rc.3
Suggested next tag	v1.0.0-rc.4

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