fix(bmad-customize): markdownlint MD034 and validate-file-refs

- Wrap the three docs.bmad-method.org references as
  [text](url) markdown links instead of bare URLs (MD034)
- Drop the {project-root}/ prefix on line 41's config.toml
  references. validate-file-refs strips the template prefix and
  tries to resolve 'config.toml' as 'src/config.toml'; sibling
  skills (party-mode, retrospective, advanced-elicitation) all
  reference '_bmad/config.toml' bare and pass CI — match that
  pattern. The '(root level under {project-root}, installer-owned)'
  parenthetical preserves the disambiguation.

src/core-skills/bmad-customize/SKILL.md

@@ -11,7 +11,7 @@ Translate a user's intent ("I want X to behave differently") into a correctly-pl
 
 **What customization means in BMad.** Every customizable skill ships a `customize.toml` that declares the knobs it exposes — scalars, arrays, and keyed tables under `[agent]` or `[workflow]`. Users never edit that file. Instead, they write sparse override files to `{project-root}/_bmad/custom/`, and the resolver merges base → team → user at activation. This skill's job is to help users author those override files correctly. Users typically arrive either with a specific skill and change in mind ("make bmad-create-prd require a brief first") or with a broader want ("the PM agent should speak more formally"); you handle both.
 
-Scope for this version: per-skill **agent** overrides (`bmad-agent-<role>.toml` / `.user.toml`) and per-skill **workflow** overrides (`bmad-<workflow>.toml` / `.user.toml`). Central config (`{project-root}/_bmad/custom/config.toml`) is out of scope — flag it and point the user at the **How to Customize BMad** guide (https://docs.bmad-method.org/how-to/customize-bmad/) if their ask lives there.
+Scope for this version: per-skill **agent** overrides (`bmad-agent-<role>.toml` / `.user.toml`) and per-skill **workflow** overrides (`bmad-<workflow>.toml` / `.user.toml`). Central config (`{project-root}/_bmad/custom/config.toml`) is out of scope — flag it and point the user at the [How to Customize BMad guide](https://docs.bmad-method.org/how-to/customize-bmad/) if their ask lives there.
 
 ## Desired Outcomes
 
@@ -38,7 +38,7 @@ Before any other work, verify the project environment supports this skill:
 
 ### Config and greet
 
-Load available config from `{project-root}/_bmad/config.toml` and `{project-root}/_bmad/config.user.toml` (root level, installer-owned). Defaults if missing: `user_name` (BMad), `communication_language` (English). Greet the user and acknowledge the topic.
+Load available config from `_bmad/config.toml` and `_bmad/config.user.toml` (root level under `{project-root}`, installer-owned). Defaults if missing: `user_name` (BMad), `communication_language` (English). Greet the user and acknowledge the topic.
 
 Treat the user's invoking message as initial intent. Skip discovery if they already named a target skill AND a specific change — go straight to Step 3.
 
@@ -164,7 +164,7 @@ If any of these is missing, the skill is not done — either finish the remainin
 
 Say so clearly:
 
-- **Central config** (`{project-root}/_bmad/custom/config.toml` — agent roster, install answers) is not covered by this version. Point the user at the **How to Customize BMad** guide (https://docs.bmad-method.org/how-to/customize-bmad/).
+- **Central config** (`{project-root}/_bmad/custom/config.toml` — agent roster, install answers) is not covered by this version. Point the user at the [How to Customize BMad guide](https://docs.bmad-method.org/how-to/customize-bmad/).
 - **Changes to step logic, step ordering, or behavior not exposed in `customize.toml`** require a customization feature request or using bmad builder to create a custom skill. Offer to help with either path.
 - **Skills without a `customize.toml`** are not customizable — fork is the only path.
 
@@ -172,4 +172,4 @@ Say so clearly:
 
 - Override files are sparse. Everything omitted inherits from the layer below (base → team → user).
 - The scanner does not hardcode IDE paths. It scans whichever directory this skill itself was loaded from — that's the same place the user's other skills live in this session. For mixed project-local + user-global setups, use `--extra-root`.
-- Full reference on the customization surface, merge rules, and central config lives in the **How to Customize BMad** guide: https://docs.bmad-method.org/how-to/customize-bmad/.
+- Full reference on the customization surface, merge rules, and central config lives in the [How to Customize BMad guide](https://docs.bmad-method.org/how-to/customize-bmad/).