refactor(pipeline): restructure config, add PromptDirectory, consolidate SQLite layer (#217)

* Refactor ApplicationOptions to separate config concerns

* add prompt dir app option

* readability updates: remove magic numbers, update comments

* codebase formatting

* Update docs

* Extract argument parsing, timer out of

tooling/pipeline/includes/services/prompt_directory.h

@@ -0,0 +1,76 @@
+#ifndef BIERGARTEN_PIPELINE_INCLUDES_SERVICES_PROMPT_DIRECTORY_H_
+#define BIERGARTEN_PIPELINE_INCLUDES_SERVICES_PROMPT_DIRECTORY_H_
+
+/**
+ * @file services/prompt_directory.h
+ * @brief Interface and filesystem-backed implementation for named prompt
+ * loading.
+ *
+ * Prompt files are resolved by key: a key of "BREWERY_GENERATION" maps to the
+ * file <prompt_dir>/BREWERY_GENERATION.md.  The interface is kept intentionally
+ * narrow so test doubles can be injected without touching the filesystem.
+ */
+
+#include <filesystem>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+
+/**
+ * @brief Interface for loading named prompt files.
+ */
+class IPromptDirectory {
+ public:
+  IPromptDirectory() = default;
+  IPromptDirectory(const IPromptDirectory&) = delete;
+  IPromptDirectory& operator=(const IPromptDirectory&) = delete;
+  IPromptDirectory(IPromptDirectory&&) = delete;
+  IPromptDirectory& operator=(IPromptDirectory&&) = delete;
+  virtual ~IPromptDirectory() = default;
+
+  /**
+   * @brief Loads the prompt associated with @p key.
+   *
+   * @param key Logical prompt key, e.g. "BREWERY_GENERATION".
+   * @return Prompt text.
+   * @throws std::runtime_error if the prompt file cannot be found or read.
+   */
+  [[nodiscard]] virtual std::string Load(std::string_view key) = 0;
+};
+
+/**
+ * @brief Filesystem-backed IPromptDirectory implementation.
+ *
+ * Each call to Load() checks an in-process cache first, then reads
+ * <prompt_dir>/<key>.md from disk.  The directory must exist and be readable
+ * at construction time; individual file absence is reported lazily at Load().
+ */
+class PromptDirectory final : public IPromptDirectory {
+ public:
+  /**
+   * @brief Constructs a PromptDirectory rooted at @p prompt_dir.
+   *
+   * @param prompt_dir Absolute or relative path to the prompt directory.
+   * @throws std::runtime_error if @p prompt_dir does not exist or is not a
+   *         directory.
+   */
+  explicit PromptDirectory(const std::filesystem::path& prompt_dir);
+
+  /**
+   * @brief Loads the prompt for @p key, caching the result.
+   *
+   * Maps @p key → <prompt_dir>/<key>.md.
+   *
+   * @param key Logical prompt key.
+   * @return Prompt text.
+   * @throws std::runtime_error if the file does not exist or is empty.
+   */
+  [[nodiscard]] std::string Load(std::string_view key) override;
+
+ private:
+  std::filesystem::path prompt_dir_;
+  std::unordered_map<std::string, std::string> cache_;
+};
+
+#endif  // BIERGARTEN_PIPELINE_INCLUDES_SERVICES_PROMPT_DIRECTORY_H_